Hey PP,
Well, since I have owned the A6 (not A5, but similar) and the RS6, I will throw my 2 cents. I found the A6 to be supremely neutral, but it taught me that I don't want a neutral speaker, I want an entertaining speaker. Don't get me wrong, I want loads of detail and clarity with nice tight (not boomy) bass, but that is not necessarily neutral.
It's hard to think of 2 speakers more different than the A5 and the RS6. With the Spendors you will be sacrificing the big bold sound of the RS6. You will lose much of the mid-bass slam that makes the RS6 so much fun. But the spendors are definately more accurate and with vocals and acoustic instruments, you gain a stunning realism.
I will tell you that I had the A6 and RS6 playing side by side for awhile and I let quite a few people listen to them. 100% like the RS6 better and not just a little better. Now, these were all quick listens and none of these people were audio sophisticates.