Peete, now that my amps sounds very well I can think to the upgrades.
First of all the opamp. There's differences about the output power or are similar?? If they're similar I choose a OPA627 that sounds good and it's not so expensive (about 10$ shipeed in Italy).
Caps: Apart C7-8 that they capacity can't be changed (right?) I've looked again your pics and I've noticed that your caps (C3-4 11 12 13) are very different from the mines. They can improve the sound?
To have a better output power an expert in electronic told me that C7-8 could be changed but cutting off the frequencies under 40HZ.
I don't know if do this experiment...
Hi netsky3, yes, those caps that are different on mine (the blue ones) are 10uF Phiilips/Vishay and of very good quality, I also use them in the power supply of my Plinius IIc preamp. They are very quiet and of excellent sound quality. The two caps, C7 and C8 are the excellent Nichicon Muse FA series at 220uF, there is absolutely NO loss of bass with these caps, which have recently used to replace some already good Nichicon FGs in two of my KHA amps, they really work brilliantly in this amp too and are a fine synergistic match for the Denon cans I prefer with this amp.
The OPA627s are fine opamps here, though with the Denons, I just prefer the wonderful AD827s as you can see in the pics. With a slightly brighter set of cans, maybe the AKGs, the OPA627s might be absolutely ideal. I can tell you that the instant the music flows into the Denons on my head, I have a huge grin on my face The Denons have never sounded so 'out-of-the-head' as they do with this amp.