Thought I added comments based on my personal experience of the Rev 5 done to my FetValve 350 EXR -- changes that I 've perceived while listening during the last few months.
The good: A welcome clarity of the mid range freq. has been improved, the mids are slightly more forward -- perhaps also because the bass is less bloated and more controlled with a little better pitch definition now.
Most pronounced change: Agree that quantity of high frequencies is more (caution here) and maybe as a result a little more extension can be heard.
The bad (being picky here) : I have perceived a small change in amplification gain with the 350EXR-5 -- I listen to music at low to moderate levels. Before I was listening at 9'oclock on the pre volume dial. Now I'm listening past 9'oclock plus 1-2 more detents on the volume pot. Don't know why-- Maybe there is a small trade-off with the Rev-5. For some reason it reminds me of a the difference of a non-regulated and better regulated circuitry.
As mentioned before, the most pronunced chage in my case has been the quantity of high freqencies. Unfortunately both set of speakers that I have (2-way), are usually known to be on the brighter side, at least with with solid state amplification. Before the R-5 mod, the non-R5 350EXR complemented very good with both SS 2010 and Vifa XT tweeters. They were a little bit on the warm-recessed side at low volume levels, but still sparkled some. I could also play loud with my 8535/2010 (DIY 39L version of the ProAC 2.5). Now the high frequencies become irritating at louder volume levels (say between 10-12 o'clock). Fortunately I can mod and change that so ultimately it won't bother me (I'll be changing that soon). However, I would be a little disappointed if I were not a DIY person and have to change set of speakers again because of the R-5 mod. So, owners of bright speaker sets are encourage to be careful here. This comment is not to downplay the R-5 mod , because I much pefer it now listening at low-mid volumes, and ultimately I know I'll have the right combination when I change my set of speakers exactly to my likes.
Again, another classic story of Audio where mix and match of components creates that final synergy of sound.
Equipment: 350EXR-5 & T7 SLR, AH! 4000/upsampler+ upgraded tubes, REL Strata III.
Speakers -- Both Homebrew (DIY):
SS 8535/2010 version of Proac 2.5
SS 8530 (Revelator 11L cabinet) with Vifa XT ring radiator w/serial x-over
