Friend of mine built a pair of SE 211 monoblocks using a d3a and mosfet follower to get 25 watts. It was such a hit at his local audio club that he's got orders for three more pairs. ;-) No one reported any audible effects of A2 drive.
It may never get to A2 with a resistive load as there is no voltage across the tube that is significant
To answer your question directly about sonics, I don't hear anything - have a SE amp that will accomodate trioded 6L6 or 6V6 types (plug and play, it has adjustable HT and bias), it definitely goes into A2 when pushed, the MOSFET follower is loaded with a CCS set to ~10mA which is plenty. 6L6s etc aren't usually much good as triode SE in A1 as the linear region is in glowing plate territory, however reduced HT and driving the grid positive fixes that.
Some 6L6 plate curves with a 3000 ohm loadline (the OPT is a UBT-3) for your interest. Note how much more linear it is when grid current is permitted, idle current 60mA at 260V at the anode.
Some 6L6 plate curves with a 3000 ohm loadline (the OPT is a UBT-3) for your interest. Note how much more linear it is when grid current is permitted, idle current 60mA at 260V at the anode.