I just listened to the SDS-XLR for the first time since the blowup, and it sings again! I didn't have any extra tubes with me because I forgot they were in Mayberry, so I had to use one of the 6SN7s that looks fried to me (ironbut had told me he thought at least one of them was shot). I am pretty sure that I need to check/replace everything to be really sure about the amp, but it does make music and I am hopeful that it will be in good form when I have proper tubes.
For those in the know, with the PS using two OA3s for 75 volts, it sounds fine without stressing the volume too much. I then tried with four OA3s and after a minute there was crackles in the left channel and it cut in and out. I turned everything off and let it sit. I then tried again with two OA3s, and the music was back and sounding good again although the left channel wasn't really stable and dropped off occasionally. I think that the bad driver can explain these things -- can't handle higher voltage, cuts on/off, etc -- but tell me if I am nuts.
All of this is consistent with Steve's experience, so it wasn't unexpected. I will get another pair of gain tubes asap so that I can try it out again, but I will probably put in all new/tested tubes so that I am sure none of them is compromised.
Nothing is easy, but I am hopefully making progress.