And that NAD doesn't get it loud enough for you? Frankly, you'd better back it down a bit or this is going to be one very short-lived hobby for you...
From my experience in MOST of cases tubes + Heresy 3 = hiss or noise. Very efficient speakers might be jeopardised by noise from tubes. The best bet is to go to class A SS amps such as used Pass Aleph 3. It may be less powerful than your current NAD, but the loudness from your speakers won't be compromised at all + you get the matching speed and thorough accuracy of class A amp to your speakers. It's also crucial to service the amp with new DC caps if it hasn't been done as they're the culprit of noise in both solid states and tube components.