I thought about going down this same road, and even emailed Burson. Two big problems with discrete op amps, though: (1) Size - there is no way to fit six Bursons in the Tobby without building a custom case. Each Burson unit is pretty big and the Tobby is not huge. As John's excellent photos show, you need to install three for each channel (total six) in tight configuration. And I'm not even including the seventh opamp for the SE output. The smaller Dexa units might work. Do let me know if you go the Dexa route. (2) Cost - the Bursons are 70-90 bucks a unit. So you are looking at a $420-540 upgrade. Worth it? Maybe if they are fit nice and snug in the case, but that's not going to happen, unfortunately. I'm not sure what the Dexa opamps cost. Do let me know if you find a supplier. As a result, I'm more interested in any possible audible upgrades to be had from normal silicon op amps. They cost a fraction of the discrete units, and fit easily onto the existing board.