admranger: If you need an amp with power and finesse Pass are definitely great amps. If a 100 watt 8 ohm amp that doubles at 4 ohms is enough for your ATCs then the ARC 100.2 will definitely work on very revealing speakers but looks like you need a multi channel amp. I used to use it on Apogee Centaurs which were pretty revealing being a full ribbon tweeters. I personally don't think later or current SS amps from ARC compete with the 100.2 and many others agree. If a Pass is in your budget it is a much better amp; has the finesse of the 100.2 but more everything... cleaner, more extended, more control if your speakers require it. There's many great amps out there and the Parasound's are very good but between the A23 and A21 you can get a lot more amp buying used in my opinion; I know these two amps. My dealer has never had a set of the JC 1's so I won't comment on those beast; those appear to be different animals which I'd love to hear someday. Can't speak on the A51 but I know they have sold many of them and I suspect it's a real nice amp but betting its signature is the same as the A21 which is a very nice amp remember so I wouldn't be afraid to try it. I've never listened to the X3 or X5's but I'd be surprised if they aren't pretty darn good. Another shop here in town used to be a Pass dealer and one of the owner uses an X3 and I believe he's always liked it.
Hopefully your Arcam is an easy fix. Good luck.