The merry go round. $700 seperates or integrated?

"I second the Audio Refinement integrated"

I'm sure the Audio Refinement is a nice integrated amp, however it would be a very bad choice for the OP speakers, Infinity RS 2.5. Excerpt from Stereophile review,

"the amplifier was current-limited into lower loads"

As I previously stated, the speaker is 4 ohms dropping much lower, and a very demanding load. It needs high current that is not limited.

Pretty sure a Cambridge 840A V2 will drive your speakers no problem. If you have a Cambridge dealer near you, see if they will let you drag home the newer 850A; if you like it then find a 840A.

Know Adcom amps well, especially the older units and their preamps. Unless you're going to spend some money to mod one, such as with Musical Concepts or if you know how to mod yourself a CA 840A V2 is a much more refined amp. 

If you're going to drift off to separates as some are suggestion I really don't think you're going to outclass a newer / used integrated. There's a lot of really nice older amps out there that are under your budget but it's now finding a decent preamp for what you have left for funds. If you don't get the best preamp you can for the money, you're wasting your time and money on an amp. 

If you can double your budget I agree you can likely build a better system with separates. 

The CA 840A V2 is not overly polite, laid back unit; so if you're wanting that look on. It is lively and has PRAT. Not bright or edgy but is revealing . Use decent cables, and PC and it will reward you. Very well built. When I had mine, I had B&K, Counterpoint separate amps as well and the 840A was much better. My speakers at the time were Apogee Centaurs which are fairly revealing speakers with their ribbon tweeters. 

Eventually I did replace my 840A but it took a ModWright 9.0 SWL and an Audio Research 100.2 to do it. I dragged home a lot of gear to outdo it; I'm lucky I have two great stores nearby that let me take stuff home. Best advice any of us can give you is try before you buy.

Go for an Adcom GFA555 or equivalent with a GFP 555 or 565 (preferred) preamp.

Alternatively, a Rotel RB980 or similar with a RC990. 

Those Infinity speakers most people probably aren't familiar with.  I only heard of them when researching an amp I was interested in that could do 250 wpc.  I kept reading about how this amp would go into protect and shut down when paired with Infinity speakers of the same variety.  

I'd be careful on the amp you select, those speakers go down to 2 ohms or so apparently.  You need an amp that can handle low impedance.  The Cambridge 840 V2 indicates on the back that it will accept 4 ohm speakers, but I can't find if it's okay with occasional 2 ohm loads.

I would stay away from Nad unless you check with the manufacturer first.  They do have a slightly warm sound, which would be a good match with ribbon tweeters, but I'm not sure their BEE integrated amps would handle ohm drops to 2 ohm.

My friend....ADCOM! used if your not worried about DAC capability...another winner is used ACURUS I have both and cant be beat for the $....with both is the much needed headroom and high current needed for low impedance loads!