The AC thread mentions that the stock opamp is Texas Instruments 5532, it is a good candidate for upgrading. The original Signetics 5532 was a great audio opamp, still available on Ebay now and then or from parts brokers. I don't know what the Clarity opamp is, but I would not be surprised if it is LM833, since they mentioned that it is from National, and that is an excellent sounding chip designed specifically for audio.
As I understand the Minimax design, there is a I/V converter immediately out of the DAC chip, which provides an extremely low impedance load to the chip, allowing it to run in current mode, which increases S/N significantly. Then the output of the I/V opamp goes to the output opamp for current buffering, then to output (or to the tube, if selected.) The buffalo designs are like this also. So the output opamp is always in the signal, as is the I/V converter.
There is a picture of the Minimax innards posted in an AC post about opamps. Iirc, there are 2 opamps near the DAC chip (I/V converters for balanced output,) but I don't remember whether there are two output opamps, or just one to sum the balanced signals to unbalanced. I guess it would be better to run two in mono even if half was unused. Then the tube runs single ended class A. So I think there are 4 opamps, but not sure.
It is very cool that the opamps are in sockets. EE knows how to fan the flames of nervosa!
