Even the +7db bass variance is still not really basshead levels. Some people even argue between needing +6db of bass in general to be neutral. That's another story all together, but essentially you'll get a very smooth linear response with no big flaws. The bassier sets will be warm and softer sounding while the more neutral sets will sound more open and balanced. If you get a bass light set, well, other than deep insertion, which might be fine depending on the user, that variation in my opinion is just overly bright and not very balanced sounding, although still fairly smooth in response, without major peaks/dips, that is, in isolated areas, just overall less bass. But it seems like the variances can either be eliminated or at least reduced based upon insertion depth.
Inserting the bass light pair very deep gives essentially the same sound as the reference pairs fitted shallow. If you wear the reference pair mid ear, the bass heavy version can be made a little closer to that by wearing them very shallow. But this is highly dependent on the user's ears, and I wouldn't assume you can fully correct either variance without first hearing each set. But it's something to try at a minimum.
As I said, I am not a basshead. I don't need huge levels of bass. IEM's I am looking for either need to sound equal/neutral and be solid at lows, mids and highs (They don't have to be great at any, just be good enough at all 3.).. Or have a nice amount of bass in so that I "forget" about the lower qualities of an IEM.
My issue with the KC06 is that while the mids are pretty damn great, the bass isn't all that good from my previous $15 IEM and the highs sound pretty awful to me. The bass doesn't do anywhere near close of a job of covering up the bad highs and it just ruins most songs I listen to. They end up not very enjoyable to listen to.
Hope that helps describe what I am looking for (At around the $60 range, though I will go higher if needed)
I think the tenores would probably work for you. At a minimum, not matter what variance, most people agree the treble is good, smooth and detailed. The bass, unless you get a very bass light version, is neutralish to warm, but both have a fairly solid low end in terms of balance with the whole spectrum. No part of the spectrum sounds "bad". And for $50 I don't think you'll find anything near the quality of these with either bass variation. Treble in iems is very peaky or dipped in even high end models. There are a few nice iems, but without knowing exactly what you consider the "right amount" of bass, it's hard to recommend anything exact. But the pfe112 is very neutral and has good bass. But it has a peaky treble up high, which isn't very bad, in fact it's very nice sounding treble, but it does have a good peak at 10khz that could be bothersome to some. The bass is considered on the light side, but I find it very reference in volume and quality for the most part.
The tdk ba200 is very nice as well, but both of these sets cost closer to $200, and neither sound as good as the tenore in my opinion. I'd risk it for $50, but obviously that is a very personal and financial decision...