Second initial impressions.
The Tenore has better sub bass. The ostry has better soundstage and openness. Things stand out a bit clearer on the otry in a direct comparison. Long term listening I find both of them become very very enveloping and details are superb, but in a general side by side, the ostry eeks out more "clarity". However, here's the catch, there is a bit of a mid drop because of this. Very slight, but the ostry are definitely a sort of "M" shape signature compared to the tenore. I'd call them a "V" shape, and they are that overall curvature, while retaining a very neutral sound.
The bass kicks a little thumpier and almost more powerfully on the ostry, without being bassier in level by much. However, the tenore is very level from bass into sub bass. For instance a few examples:
In Surround by BT and Aqualung, at 2:20 the sub bass drop sounds so great in the tenore. On the ostry it starts off with nice sub bass, but gradually decreases in level as the bass drops so by the bottom half of the bass drop it doesn't sound very impressive. Not that is sounds bad, and you can hear it down to the lowest tone, but it doesn't sound "impressive" like the tenore in that area.
However, in a song like Sailing by Christopher Cross, the treble and mids of the ostry sound more open and realistic, such as at 2:43. The piano and everything sound like they're in a more realistic space. There is depth between instruments a bit more than on the tenore and things just sound deeper, larger, more spacious in a sense, but not really brighter.
These two songs really are a good example of the main differences I'm coming to find between the two. If I had to say which I thought was more reference, I'd probably say the tenore, because it extends so far in both directions and is very linear in response.
The ostry is a very close second in that regard. However, the ostry has that greater sense of depth, attack, openness, etc. that gives it a very nice edge. So I'm sort of torn between the two. I wish the ostry had better extension on both ends and a touch more mids. Or I wish the tenore had a bit more depth and impact or attack force behind each note.
The differences are small compared to other iems. It's like changing a filter on an iem vs changing one brand/model to another. They share a lot in common I think. Some people might not hear it this way, because even though the aren't very different, those differences can have a huge impression upon different listener's based on their tastes and listening habits, etc.
I'm enjoying the heck out of both of them and might still get an ostry, but I'm not so keene on letting go of any of my tenores. haha. I'm so selfish!
The tenores also provide a bit more isolation. Whereas the ostry don't realy allow much isolation in general due to the way they were designed to fit. I get a very consistent sound upon every listen because of this design, but unfortunately it means very little isolation. And while the tenores may not reveal as much depth and distance between things, I don't really consider them less accurate in that regard. Whether it is a difference in speaker presentation or just frequency response I don't know, but I find that a flat response like the tenore renders depth beautifully when it is recorded well. So does the ostry, but a find a lot of the ostry's depth and whatnot comes from the slip dip followed by a slight mid/treble boost. This is a very common frequency shift that enhances depth and soundstage. Just take a look at a graph of the sennheiser HD800. Exactly that.
However, I find personally that anytime you shift the frequencies like this you end up getting at least some masking of frequencies. The tenore for instance will render a guitar in the midrage in a complex passage and it will be as audible as everything else. However, the ostry will make that instrument a bit harder to pick out. But the ostry will make all of the other instruments sound more dynamic, deep and spacious. So one thing takes a little from the other. Whereas the tenore might sound flat and boring on a certain track, but every instrument is easily discerned. While the ostry renders the track more "beautifully", but certain things won't sound as noticeable or apparent. But on the other end of the coin, the tenore might blend everything evenly as mixed, where the ostry might make certain things "stand out" in a way you didn't really notice them before. So they almost sound "enhanced".
Again, I believe this is all a matter of frequency response and not any magically specifications or sound properties that people usually cite as the cause. If I boost my tenore in the 2-8khz region in a certain shape, they bring out just as much detail and depth and whatnot as the ostry, and even sound better in my opinion, because of the overall smoothness otherwise in response. So it appears to me these iems are very very capable and very similar, but with slightly difference frequency responses and different fits, isolation, appearance, etc.
Lastly, the tenore sounds smoother in every way. I don't just mean response, and I'm not saying the ostry is "grainy" or anything. It's just after listening to the ostry for a minute and then putting the tenore back in, it's like everything is "cleaner" in some way. I don't think it is distortion level or anything. Perhaps it is micro variations in frequency response. I'm not sure. But it's a noticeable difference as much as the depth of the ostry is a noticeable difference to me.
I'm still not sure which I actually prefer when it simply comes to enjoying music. Part of me says the ostry, but then there are songs where the sub bass and airiness of the tenore are just so nice. Hmmmmmmmm.
EDIT:
A quick pro/con list:
Tenore Pros: very neutral (with reference set), very small, comfortable, lightweight, excellent sub bass and high treble extension
Tenore Cons: Not much.
A bit less than ideal in depth/soundstage, less than ideal fit consistency.
KC06 Pros: a nice gentle V shape that enhances overall depth, etc. comfortable, easy fit consistency
KC06 Cons: Lacks perfect sub bass linearity, V shape is slightly more than neutral (might not be a con), bad isolation
I can hear now how some people might find the ostry a bit more resolving in fine details. I do find things "stand out" more with texture and clarity in certain ranges, while not really detracting from the mids. Very nice signature in that regard. And despite having more general bass and treble in that V type signature, the ostry's sound a touch darker to me overall. The tenores have more airy treble and more mids, which give them a sort of flat to 'light' sound. The ostry have slightly more powerful bass and the boosted treble region, but they almost have a more tilted downward treble slope above the main section of the treble, this lends itself to a bit darker sound in a way, but only slightly.