Maybe it's just a matter of perception but I have all valve, hybrid and SS amps. The difference with the all valve head is that volume gain seems to be more linear as you wind it up and stays full and fat sounding with a bit of tube distortion, whereas the hybrid (class D) and SS stuff seems to get more 'shouty' and increasingly brittle sounding. 200 watts of valve power easily keeps up with 600 watts digital or SS. Could well be complete rubbish, but that's how it sounds to me.