I have actually played CDs in my HD-A1 player, and disagree with George's guesses, to a point.
I don't know what kind of CD player you are used to, so even though I have played CDs in my HD-A1 we have no common comparison that I know of, but here is my best try.
I would rate the HD-A1 as GOOD. Not bad, definetly better than the typical $300 CD player or 5 CD Changers, but not quite as good as my Denon 3930ci. The Denon has actually been rated as a pretty good audio player, and I would put the HD-A1 a little below it.
Now I wouldn't compare the HD-A1 with say a Rega Apollo, but I think it would compare well with any stand alone CD player in it's price class ($500 new - $250 used).
The HD-A1 brings out a fair amount of detail, with just a little harshness. IT also does a good job with DTS DVDs.
I think the HD-A1 does a good job of Upscaling SD DVDs. I do use my Denon 3930ci for SD DVDs but sometimes I question this. The HD-A1 seems a little sharper, but I prefer the 3930ci color a little better.
If you post what stand alone CD and DVD player, we may be able to give you more feedback.