You aren't going to see issues at -20db levels. But, if you run at -10db and above, it would be good insurance. I did blow out my older KL650s with a receiver amp. They had similar impedence challenges, and I pushed too hard.
Sound quality improvement? Maybe ever so slight at normal volumes. Up near reference, the difference in dynamics will be clearly detectable and it will be safer.
I run my rs62s on an XPA5 and they haven't complained about anything....and they've been run through the paces.