Dan,
I went with opa627 ( digikey ) in the outputs (1 and 2 but may do others ) and replaced the tubes at the same time for a subtle improvement. I believe the op amps are much cheaper on ebay if they are the real McCoy? I expect a greater jump with the Obbligato's as that's when others say it all comes together. Are you using 12ax7 or 12au7? Can you provide a link to the Panasonic caps you used on the PS?
Thanks, Paul