I was in the same position you were in Apoq. I bought some the two Burson op amps, and they would have a loud hum when placed in the U5 position. I was not impressed by the Burson op amps. If I replaced one of them with another SS op amp mentioned below, the hum would go away, but still close to the definition of a SS op amp.
This is what I originally did, bought a GE 2c51 tube, the bass response seemed to extend a bit. Then I bought 2x LT1364 op amps, both were good, although not as refined as I'd liked them to be. Then I bought 2x LME49710ha and soldered them onto the brown dog adapters to convert them into DIP-8. They were OK at best, but I still preferred the LT1364 since the LME49710HA seemed to have a V-shape EQ curve. Then I bought 2x lme49860na. I tried putting both the lme49860na in the U5 and U6, but the wide sound stage seemed to disappear.
My perfect combo so far is: 1x lme49860na and 1x LT1364. The amp is currently with a friend at the moment, so I can't tell you which goes in the U5 or U6. You'll have to try and experiment. Personally, I'd say away from the LME49710ha, even though they get high praise. The LT1464 is roughly $7 each from digikey, with the lme49860na being roughly $3 each. I think they're cheap enough for you buy 2 of each and it'll be roughly $24 with shipping.
http://www.digikey.com/product-search/en/integrated-circuits-ics/linear-amplifiers-instrumentation-op-amps-buffer-amps/2556125?k=lme49860na
http://www.digikey.com/product-detail/en/LT1364CN8%23PBF/LT1364CN8%23PBF-ND/891887