Upgrading from NAD 320 BEE?

NAD C355Bee new (80wpc), NAD C372 used (150wpc), Cambridge Audio 650A new (75wpc). All of these amps are ridiculously good for the money, and your B&W speakers will benefit from the added power.

If you go down the upgraded phono amp route, then on the lower end of your range you must think about the Bellari VP130 if you intend to use MM cartridges. This units sounds really nice.

The upper end of your range is crowded with good deals like these:

Lehman Black Cube Statement
Grado PH-1
Musical Fidelity X-LPS v8

or, if you can spring for a little more, look at the Musical Surroundings Phenomena II - or try to find an original Phenomena used.

Good luck.