Don't think they let you privately sell your old equipment through here. Try going to http://www.canuckaudiomart.com/ or one of the like sites for USA and europe

if you want to trade in your M80 and buy some newer ones, then the trade in is an option. You put in your serial number and they will let you know how much you'd get. Up to you if you trade in or sell privately. Pro's and cons to each

Anthem: AVM60, Fosi DAC-Q5
Axiom: ADA1500, LFR1100 Actiive, QS8, EP500, M3, M3comp, M5