Hi Derick, I got your e-mail.
Actually, I've only tried one amp with the 2.5s. The BAT VK200. A year and a half ago when I was running ProAc 1SCs I did a shoot out with some amps that included the VK200, Blue Circle BC22, an older Bryston 4B and a Pass Aleph 3. The preamp used with all amps was the Blue Circle BC21.
My prior experience with ProAcs [Tab 50 Sigs and 1SCs] showed that careful amp matching was necessary. The ProAc tweeter can be bright and I didn't like the results when using all solid state amplification.
Around three and half years ago, after doing a lot of forum reading I decided on the Blue Circle BC21 tube preamp and BC22 solid state amp combo. My reasoning was that a combo like this would provide three things I was looking for. Warmth, power and minimal tube hassle.
I've owned the 2.5s for abour nine months still enjoy using a tube preamp with a solid state amp. I have thought of trying other preamps such as the First Sound Presence and other solid state amps like the Plinius SA-102 and McCormack DNA-1.
I'm sure the First Sound would introduce a level transparency my room has never experienced. However, there's something about the older BC21 with its 6SN7 tubes Ive grown to love. They produce a rounder, warmer sound than the 6922 tubes the Presence and other preamps I've tried like the BAT VK3i use. It really depends on what you're hoping to gain.
While I enjoy the the power and ease of use solid state amps can provide, I have become curious about lower powered SETs, possibly as a second amp. While ProAcs don't have the best measured sensitivity, I've heard they have a fairly gentle impedance curve that makes it easy for some low powered SETs to drive. One amp in particular I'm eyeing is the Wright Sound Mono 10.
Good luck!
Dean