Infinity RS IIIa

What's the difference between Infinity RSIIIa and RSIIIb ?
I just bought the RSIIIa. I don't have any pwr amp for the RSIIIa yet. I just use my old denon avr-3800 to drive them and sounds just fine, the amp does not hot but needs to be put on high volume level.
I have Paradigm studios (100v2 & 20v2) in living room and 40v2 in bed room, powered by Rotel.
I seems Rotel good enough for 100v2, Do they good enough for the RSIIIa ?
I like the Infinity because of their "air suspension" woofer, sounds different from "bass reflect".
I had infinity kappa 6 for years until I sold them 8 years ago. This RSIIIa brings back my memories....
The RS IIIa is a good speaker and easy to drive. Any of your amps should work. This is because the woofers are wired in series, so the ohms are not too low. If the woofers have never been refoamed, then check the surrounds for tears and cracks. This speaker is very flexible for set-up and OK for small rooms or close to walls for extra bass. I will ask my friend if he remembers the difference between "a" & "b" but I don't think it was a big change. I think the sides of this speaker are very attractive with the oak trim. If your woofers need refoaming I have a set that were redone a few years ago if you need them. I believe this speaker sounds fine aimed straight ahead or very little toe-in.
Happy Listening, JAY