New amp recommendations

Hello. My current amp is a big old Onkyo M510 Grand Integra. The preamp is an Italian Musical Technology c2. The speakers are Proac Response 4.

I would like to change the amp. Any good amp recommendation for the Proacs?

Finally, what if I keep the Onkyo? Any suggestion for a good preamp to pair with it? Thanks.
Check out the review in The Absolute Sound for the Musical Fidelity M6CD/M6PRE/M6PRX. You might want to consider the M6PRX, which is a seriously fine amplifier ($3500 list new). In the TAS review, the author specifically mentions Proac as a good pairing. There's a used M6PRX for sale on Audiogon right now (the first one I've seen come up) for $2100 which is a terrific value. I have no connection with the seller, but I do own an M6PRX so I know what a great amp it is.
I think ProAc uses Audio Research in speaker development/voicing. That should be a place to start.

I can't recommend anything because I have no idea what your budget, room size, preferences, etc. are. Just threw out the ARC recommendation due to ProAc's use of them.
Some additional background and input: the size of the listening room is approx. 450 sq. feet, music that I listen to is pretty much everything other than metal and rap, budget: max 5k. Thanks!
I think a Parasound A21 will work great for you. It will save you $$$ for more music and other accessories.
just to be contrarian, (unless of course you want to sell it to me) i'd be really reluctant to replace your integra amp--it's a fantastic sounding piece which would cost something like $8k in today's bucks. to be honest, i've only heard it paired with pre-amps of similar vintage (like the integra 308), and i haven't heard it with your (excellent) proacs so i can't recommend a specific modern preamp, but at your budget you can afford to experiment a bit (tubes? passive?). kbarkamian's idea for ARC makes some sense.
What would you think of pairing the integra with an ARC Ref 3? In addition, do you think that Audience AU24 cables could be a good match?
5k in what currency ?? US$ ?? £ ?

Moon integrated in your bracket is worth checking out. Or if you can find one at a discount the Gryphon Atilla .....
Pairing a REF 3 with the Onkyo would be like mounting Walmart tires on a Ferrari.A more balanced approach,consider an Audio Research tube amp at the 2K to 3K price point.
I've found a nice used REF3 for a reasonable price. Should I get it? Also, can you please recommend some good, reasonably priced speaker and IC cables? I've heard good things about Emprical Design cables. Thanks.
I agree that matching a REF3 with an Onkyo amplifier is a bit of a mis-match... but who cares. This is a hobby and if you want to give it a try, go for it.

I think it makes more sense to buy a component that you really want (like a REF3) and plan to keep, than buy two components which you know you will flip down the road and possibly lose money on.
What about the smaller ar ls26?
Keep the Onkyo, you are not going to gain much if anything replacing it with another amp from an audible standpoint unless your just looking for more power.
I'll keep the Onkyo amo. Still undecided between ARS LS26 and Ref.3 preamp (both of which I will try to audition). Is the Ref.3 worth 2k euros more than the ls26 (used)?
For the same money - less actually you could get a Audio Research VSi60 Integrated. Very nice sounding amplifier.
Grimace, thanks but I don't need an integrated amp. I am looking for a good preamp to match my onkyo amp.