What type amp to drive proac response 2.5

The great thing about used equipment is that you can keep experimenting until you get it right, and for a minimum cost if you buy carefully. I think you should buy some tube amps you think you can resell with minimal, if any loss, and see how they sound. Quicksilver or Music Reference would be my picks. Preferably something with an EL-34 tube.

You should be able to find a very nice tube amp for that price. 60 watts ought to do nicely.

You can find refurbished Harmon Kardon Citation 2s for that price.

There is a pair of Quicksilver Silver 60 on Audiogon now. I have no affiliation and do not know the seller. I just saw the ad.

The ProAc 2.5s were the speakers I owned longest over about 3 years. I used them with Sonic Frontiers Power 2, Levinson 331 and Plinius SA 100mkII. The Plinius was the best match, especially when switched to Class A. All of these are going to go beyond your $2k budget. These speakers need power and current. The only amp I did not get to try and was told it would work quite well was the ARC Vt100 mkxx.