Then gain cannot change from the mod. It must be because of the difference in firmware.
The poly caps are probably placebos, as Cyril Bateman's very careful measurements (published 10 years ago or so in Electronics World) show that parallel poly and polar electros don't reduce capacitor distortion very much at all, far less than using a nonpolar electro (or a full-sized poly, which is lowest). The problem being that there probably isn't room inside the case for nonpolar electros because they are slightly larger (or full-size poly, which are a lot larger).
A quieter opamp can improve EIN by reducing input stage noise if the rest of the circuit is designed in a manner to allow for an improvement. But that might only be realized at gain settings higher than would be used for condenser microphones, especially for amplified concert recording.
Hmm. Based on what I read in a few posts here, I was under the impression that even these smaller poly caps would help reduce phantom noise since they do that better than electrolytics. I will try to track down that article you mentioned.
FWIW, I only decided to go for this mod because I record almost 100% acoustic music, and other than marching band season, most of it is relatively quiet (choir, chamber groups) and/or very wide dynamic range (band, orch large choir). I would expect zero audible improvement with this or any such mod at low gain, recording amplified concerts.