Just seeing this thread now, thus the late reply.
I have no experience with the SS2590s. These are large opamps that I would use only with great care in a component with a closed case (assuming they fit). They're described as being powerful. Someone posted about his experience rolling the SS2590s into the Geshelli DAC. One of his comments stuck with me--said the volume/gain of the amps single-ended output rose noticeably vs the XLR outputs. That means more power, and more power probably means more heat...?
I do, however, have experience with Sparkos' SS3602 dual opamps, I rolled a pair into the preamp/output PCB of the Violectric V281, which has been my go-to preamp for my main office system for years; and a couple weeks ago, I rolled a pair into the headphone outputs of the Violectric V280.’
The sonic results with the V281 were immediate and positive, though admittedly fairly subtle, not earth-shaking. I’m still evaluating the sonic effects of these opamps in the V280.
I’ve rolled other opamps before, but these Sparkos' are the best I’ve heard. I’d love to try the SS2590s, but am hesitant only for the reasons given above.