I believe you would be happier with your 2.5's. I had them, as well and can give you some advice on how to get more out of them. Your Rowland is a good match for the speaker, but not the best. Its a very unusual piece. I have a Rowland 112 which I think is very similar, or even the same amp that is in your integrated. The Rowland is very detailed but also, at the same time, very forgiving. You really don't need an amp like that for your speakers. Its a good amp to use if you need to "fix" a harsh or bright speaker. Your Proac's do have a very musically forward, lively sound. Your amp is holding back a lot of that. Your Arcam is also a very good piece. I had the 33 but imagine that there isn't too big a difference between them, as well. It has a very "polite" or smooth sound but not a lot of dynamic contrast. You could say that the Arcam, generally speaking, aims for a similar sound as the Rowland; but not taking it that far.
If it were my choice, I would upgrade your amp first. Tube or solid state will work fine. You just need to pick the correct amp regardless. Heres a list of tube amps I used that will make a huge difference in sound quality: VAC 30-30 Mk III, Quicksilver V4 Monos, Audio Reasearch VT 100 (1, 2 or 3 - all good). For solid state: Ayre V5, Bat 220, Pass 0's and CJ 2250. I'm sure there are some other good choices as I haven't herd everything out there.
In my opinion the best tube were the V4's followed very closely by the VAC. For solid state, the Ayre would be my first choice. Any of the amps I list, though, I think will be a much better match for your speaker than the Rowland. Your system will immediately come alive with any one of them. For the rest of your system, I say keep the Arcam, for now and get a simple passive preamp so you can use it. From there on, I would listen to the system for a while and get very familiar with it. How you deal with you preamp in the future will be very important and it would be best not rush into it quickly. It will make just as big a difference at the amp.
Hope this info helps. If I'm not clear on something, just post and I will try to give a better answer.