They're both very good units. I own and love the Rotel RQ-970BX. I'm on my second one, in fact. I've had more expensive units but I've found you need to spend between $500 and $1000 before you get into significant across-the-board improvements. The Rotel's $199 MSRP has not changed in many years, making it an even better value than ever.
I owned the original NAD PP-1 and found it good but a little dark sounding. The Rotel is livelier and more resolving. It all depends on the rest of your system.
Don't count out the Cambridge Audio 640P -- also around $200. Many people feel it's the state of the art at this price point. I don't have extensive experience with it but knowing Cambridge products in general, I'm sure it's an excellent value provided it gels with the rest of your system.
Good luck!
I owned the original NAD PP-1 and found it good but a little dark sounding. The Rotel is livelier and more resolving. It all depends on the rest of your system.
Don't count out the Cambridge Audio 640P -- also around $200. Many people feel it's the state of the art at this price point. I don't have extensive experience with it but knowing Cambridge products in general, I'm sure it's an excellent value provided it gels with the rest of your system.
Good luck!