I've had a lot of experience with the Boston line - several pairs of A40's, A70's, A100's, A150's (2 pair), a400 (2 pair), CR7, CR8, and T830
I currently have a pair of A40's and the only reason it's still here is that it didn't sell at the garage sale this weekend
Not to say that the Boston's are a bad speaker, in many respects they're really nice sounding. Just not keeper sounding to me and when you factor in things like looks, vinyl veneer for the most part, it's an easy decision to part with them. It's probably me, but I've always found the Boston tweeter to be a little too hot and fatiguing for my ear
Soundwise nothing memorable sticks out as to the differences between the CR8's and the A40's If you like the sound of the CR's I'd keep them as a move to the A series would just be lateral (unless of course you came into A400's) But if you're trying to stay in a particular size range like the choices you've mentioned maybe look at an EPI 100 (walnut) - JBL L20T's L1's (I like the t35 tweeter but to others it screeches)
Ampwise I don't think an upgrade will have much of an affect on what you currently use Sounds to me like you just have an itch to try something new Speakerwise I would look outside the Boston line and ampwise I can't give advise that way