Andreas
Some background ...
The C350 was discontinued about a year and a half ago and was replaced with the C352. The C350 was a very popular product that performed very well and usually garnered 4 or 5 stars (out of 5) from most amplifier shoot-outs that the British hifi press did. The new C352 offers a bit more power than the C350 did (80 wpc as opposed to 60 wpc).
The C320 BEE came out about 2 years ago and incorporated many of the amplifier tweaks that NAD had been introducing in its more expensive products since 1998 or so, which the 350 did not incorporate. The BEE designation was also marketed as a special distinction. It represents the initials of one of NAD's original and senior designers (Bjorn Erik Edvardsen) and represents a product that offers 90% of what a product that costs 10 times as much would offer.
The improvements of the C320BEE over the C350 included: NAD's PowerDrive technology, which in theory makes a power supply act like it's much larger, leading to improved dynamic power. NAD also tweaked the circuit design, with an upgraded toroidal transformer as well as smoothing capacitors.
The C352 now offers these improvements.
From here, it gets easy ... one question really. Do you like the "house" sound of NAD integrated amps? There is no mistaking a NAD for a tube amp. As you can tell from the opinions expressed so far, there tend to be love em' or hate em' responses. I have owned a C320BEE for two years with no problems ... it plays louder than its 50 wpc would have you believe. It also does a very good job with most music types ... good detail and musical sounding ... but definitely, not the most refined or elegant sounding amp (as compared to my Musical Fidelity amps).
I believe that you have to exercise some care with what components that you match NAD amps with. I have had very good luck with the Music Hall MMF CD 25 cd player and acoustic suspension design speakers (AR 302's and NHT SB2's). You also need to use decent cables, like Better Cable Interconnects and Signal Cable speaker cables.
The C350 is no longer manufactured ... so, there is no reason to chase it. The C352 is a step up power wise from the C320 BEE and most likely includes the latest tweaks. You can't go wrong with either one. What equipment do you plan to pair the NAD with?
Regards, Rich