Hello, oldzorki.
I think I can partially answer your question. I have never driven Gershmans with my IDA-8 (or any other amp), but my speakers are 83.5 dB sensitivity - though due to the series crossovers they are easier to drive than 'regular' low sensitivity speakers.
I've had a couple other amps drive these speakers, so I have a pretty good idea of how it compares (at least to the other amps anyway). I'd say that the IDA-8 does a decent job of powering my speakers if I am not trying to listen critically. To be fair, most of my music listening is non-critical because of my room, my habits, and my dear wife. It is only when I want to really listen, really pay attention to the recording that I realize the 100 watts isn't giving me all the speakers are asking for. Mind you, I'm not listening at unreasonably high levels either.
If I could re-engineer my IDA-8, I'd replace the 100w amp with the ST-10's amp [Would that make it an IDA-10?], or with a nice EL34 tube amp. Either mod would probably make me a pretty happy camper.
I really like my IDA-8 and I really enjoy its features. I have my Squeezebox Touch feeding it wifi from my Mac Mini, Bluetooth from either my iPad or iPhone, and my TV feed via optical. It's amazing how much this amp offers especially considering its very reasonable price.
If my speakers were 87 dB to 90+ dB, I would be enthusiastically telling you to rush out to buy an IDA-8 (because it's that good), and I wouldn't be telling you about its shortcomings.
Enjoy your search.
Michael