In a word, the LPA-1 and RPA-1 sound neutral, fast, and dynamic. They have clarity and detail. The RPA-1 punches well in the low octaves. (Can't comment on the LPA-1 in this respect - I use it in movie mode i.e. the sub does the low bass work.) It plays well above its perceived value.
The RPA-1, driving Vantages, reminds my of my CIA monoblocks. It has a similar sound signature. Whenever I inserted the RPA-1 into the system I thought, surprise, that's fine, I don't think I miss the D-200s. A few weeks later when I put the D-200s back in I thought, yes they do do everything a little better after all. They have more of the elusive PRAT, and all the other stuff which makes you tap your toes, twitch rythmically in your recliner, pull weird faces, do a little jig. A few weeks later I went back to the RPA-1, and I was back to, surprise, that's just fine, toe-tapping, twitching and all.
In other words, I have not conducted an A/B test yet, like I did with the RSP-1 pre-amp vs my passive line stage. I agree that's very unscientific. FWIW, I believe that I enjoy the D-200s more after all. But isn't the fact that I did not feel compelled to do an A/B quite telling in itself. The RPA-1 certainly is not bad at all, independent of price.
Now factor in the superb build quality, the looks, features. Then look at the price. Gasp. $450 for an LPA-1? $700 for an XPA-2 or XPA-5. The RPA-2 price will be in this ball park also. (I got my RPA-1 on a sale for under $550 shipped - well I bought the other stuff, too. Under the skin the RPA-2 will be its twin.)
If it is your habit to listen at loud volumes, make sure you have dedicated circuits feeding each amp. I hear these amps want Amperes when driven.