Several of the above op-amps are available in 8-DIP configuration so that they will drop directly into the EE DAC without the need for Brown Dog adapters, as follows-
(check with Digikey)
OPA627 (single) can drop right into U6/7
OPA2134 and OPA2604 can drop into U1/2.
And remember that if you use the tube out only, the U6/7 op-amps aren't used so don't bother to upgrade them (pretty sure about that).
I have been using the 49990s for a while now in SS mode (original DAC) and still like them very much, but all this talk is getting me itchy again...