During my bout of insomnia early on Sunday morning, I placed an order for the Burr-Brown 2107 as well as the 2111. Hoepfully, I'll get these this week. But, I do have to say, even with the stock op-amp, my latest tubes, the Voshkod 6ZH1P-EV (about $40 shipped for a new pair from YenAudioStore), I'll have to say that the sound is just sweet to my ears.
Fortunately, the op-amps are somewhat cheap to try and see how things sound. Getting the OPA627 from Burr-Brown is supposed to be a great op-amp too. However, you'll need two op-amp chips and a Brown Dog adapter. But, there's a big risk of getting some counterfeit chips too as many from China are just that - fake. Instead, buying from DigiKey, Mouser, etc. might be a better alternative on the 627, though I havne't read too much on that chip with the Little Dot. Finally, some people have sourced the OPA-627 from some older audio receivers before tossing them. If manufacturers such as Yamaha and their older audio/video receivers used the chips, you could get a pair that they used for each channel. I think the 627 has been around a long time (15+ years?) due to the popularity.