I think the 846 is near perfect with (right now) modded blue filters EXCEPT that treble is slightly rolled off for my tastes. It's there, it certainly isn't grainy or scratchy (?!), there's just not enough of it for my tastes on a lot of my music. Now those tracks I have that have a bit too much treble, and a lot of the live stuff I have that is soundboard but a bit bright, THAT sounds great with the 846.
Waiting for my UERMs to arrive. I'm going to miss the double thump of the 846 (remember I'm running a Pono in balanced mode) but when I demo'd the UERM in single mode (I asked for a balanced cable, sent them the Pono tech sheet, and was just told they are going to begin making them) it sounded very good in the bass area. Just not like a freeway rumble. And mids and trebles were much clearer and more extended.
I've really enjoyed my time with the 846 using my Moon AudioSilver Dragon cable. An almost perfect iem (for me).
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I finally molded the blue filter and listened for two hours.
The impression of sound difference when paired with AK120II in balanced mode with pure copper cable using stock olive tip:
Using Fleetwood Mac's rumour DSD files, treble extended further without harshness, vocals is more forward and clear. Bass is not so booming and punchy with greater detail. Overall perceived volume output is greater than before. I like this sonic performance.