Denon D-M31 CD-Receiver

My wife has one on her desk and it's pretty nice. I reviewed the predecessor, DM-30, in Stereophile a while back.

For the same price, Yamaha mini-system is better. It plays louder and clearer. Bass is a little too enthusiastic and thumpy for my taste. But it is a larger box than the Denon.
So I'd suggest letting her listen to both at Tweeter's or Ultimate Audio.
The big problem with the UDM-31 is the DAC. I'm not a big believer in large differences in digital but the Denon DAC was so bad, I would likely upgrade it to a Scott Nixon DAC for $100.00. Notice the better ~$600.00 Denon moves to a separate CDP.
A better speaker will merely show this problem even more.

For $1,000 I'd get the Epos, Monitor Audio Bronze, B&W 601, or Ascend Acoustics CBM-170 for $328, a refurbed Harman Kardon receiver ($190.00 at www.harmanaudio.com), NAD, Toshiba, or Marantz CDP. The whole system would run about $700.00. If she can live with a larger system.