Yes folks, it's that time of the year when I get some, at first thought, strange email request that on further investigations turn out to be useful. In this case it has been about the Gator. I'll skip the preliminaries and go straight to the finals .

Non-headphone users who own or are looking at a Caiman/Gator combination:
The choice of opamp is unimportant. So you can stick one of the LM4562 from the original PCB in there.

Headphone users with Caiman & Gator:
The AD826 wins on all accounts so far. No messing about with special adapters (i.e. THS4032 ) or bending pins ( i.e. LM4562HA).

Non-headphone users with TC-7520 & Gator:
The original NE5532 is good enough in the headphone slot.

Headphone users with TC-7520 & Gator:
The Caiman PSU or any good 15V PSU like the linear one from Maplin is a must.
Opamp choice, after a lot of experimentation, is the LM4562NA as used in the standard Caiman. I have tried things like the AD826 and THS4032 instead, but the TC-7520 sounded far too dark and bass heavy. Good for getting my D7000 cans to rattle my skull when fed with some bass tracks, but Norah Jones sounded drunk and randy. I prefer a more even handed sound...

If you must have more extended bass (down to about 5Hz on my scope ), on the Gator there are two sets of empty components holes. It's obvious they are for capacitors. You can try a set of 100uF or even 220uF non-polarized caps. Don't use polarized caps.

Swapping out the caps on the Gator for a different type:
DON'T. The first and only person to have tried that has had to acquire a new Gator PCB.

Changing the gain on line out and headphones:
I'll come back to that at a later stage if there are sufficient interest. The current output levels are designed to be within the CE limits, but the line and headphone output especially can be adjusted for a different optimum gain setting, depending on the impedance of your headphones. I use one Gator set up for my D7000 and K701, and a different Gator set up for my HD650 and HD800. But not everyone would need to be so pedantic as me.