Difference between Phonak Perfect Fit and Perfect Bass?

Yes, it is just filters and accessories, but the grey filters IMO are way superior to the others, which veil the sound a bit and drop overall clarity and sparkle - and clarity and sparkle are really the main reasons to buy these IEMs.

PFE EQ well without distorting, so if you want more bass, better to use the grey filters and just eq yourself some more.

http://www.head-fi.org/forum/thread/519356/review-phonak-aud-o-pfe-022-perfect-bass

Had PB with black and grey filters bought separately.

To my unsophisticated ears differences in sound between filters are rather subtle, especially between greens and blacks. Vs blacks greens bundled with PB result in a signature that's somewhat more smooth, warm, with a little more bass (still anemic to my tastes) but at the expense of some detail in highs and maybe a little less forward mids and a bit narrower soundstage. But it's all splitting hairs unless you are a bona fide head-fier.

Compared to both greens and blacks grays are more unique, but still well within same overall sound signature. To me grays sounded with most detail and clarity in mids and highs but with the least amount of bass. Still if you are into "neutral, balanced, uncolored" school of sound and corresponding music which isn't "un-balanced" by definition even with grays bass should be enough.

No matter which filter sound sig of Audeos stays more or less the same at its core - polite, balanced, detailed, forward, non fatiguing, no excesses, with rather intimate and shallow soundstage. Not really satisfying and fun to my tastes but technically I guess great.

Oh and another tidbit. Audeos are relatively inefficient out of iPod/iPhone and actually benefit form the amp (at least from my stationary Creek OBH-11). But to me gray filters seemed to be a bit easier to drive than greens probably because of the need to move less air.

As an aside, the PFE112 are the survivors of my collection. They were the first £100+ phones I got and a good few other expensive phones have been bought and sold and traded and they're still standing - I just never get bored of them. 

i miss my pfe's... maybe its time to buy them back. 

I bought a Phonak Audeo Perfect Bass Earphone several months ago & I am extremely please by their sound quality. I am running them straight out of a Cowon D2+...all my music is in flac and the sound quality is very good. Also about the fit (at least according to my ears with medium tips are perfect). They are also so small & light you don't even know you have them on.