About 2.5 year ago I bought a used 950 off eBay and used it for about a year.
Then last year I replaced it with the 990 (as well as my Adcom Amp with the 7125).
I would say that the 2-ch CD sound is MUCH better than it was before.
I am using the Upsample mode, which really makes a difference.
For movies, the sound is also better than with the 950, and there are more options in the menus.

I would suggest geting the 990.
You can use it with your current amp, but the 7125 works quite nice with it.