Hi Mike,
What Cayin Amp are you considering and what CDP are you using?
A couple of months ago when I picked up my new Heresy III I had the opportunity to listen to them connected to a Cayin A88T tube amp and a Cayin CDT-17A tube CD player. To my amazement these Heresy III sounded totally different to when I had them hooked up to my Denon 5803. It sounded like there were Subs in the room, I couldn't believe the depth and loudness of the bass, neither could the store manager. The sound was floor to ceiling and wider than the room with absolute detail and you couldn't detect where the speakers were placed. After hearing them connected to the Cayin Tube Amp you might decide you dont need a sub.
ATM I have them hooked up to a Onkyo SR701 and using a M & K V75 sub and they sound good but nothing like when they were connected to the Cayin tubes.
So it looks like its tubes for me in the near future. Is anybody on the forum using Cayin amps or CDP?
Regards Skeg.