Either amp will be fine but for a room your size,I would opt for a more powerful amp,say a C355BEE.I have not heard the T5 or the T6 but I have heard the T65 and I thought it sounded great for the money.I highly reccommend you try to audition the equipment if possible.These are 3 NAD authorized online retailers.Spearitsound, DMC Electronics and Saturday Audio Exchange.I have done business with Spearitsound and was totally pleased.DMC and SAE sells NAD and PSB.I think if you contact either and talk to them about your needs they will help you.As inexpensive as NAD and PSB is,I would opt for new equipment with the peace of mind knowing you have a warranty,but that's just me.OTOH,buying used will save a bundle of money if a warranty isn't important to you. NAD and PSB are owned by the same parent company and work very well together
https://dmc-electronics.com/Default.htm
http://www.saturdayaudio.com/
http://www.spearitsound.com/
https://dmc-electronics.com/Default.htm
http://www.saturdayaudio.com/
http://www.spearitsound.com/