It's pretty similar to the 797 actually, just mo better. It also sounded quite nice with the RCA Clear top, but I don't have he Fullmusic tube to compare. I always thought the 797 was a little on the "lean side" I prefer the bass of 49990. This is very subjective so it's pretty hard to compare op-amps and tubes. I think 49990 is worth a shot for you, but I wouldn't bother with the other op-amps I've listed. Ad743jn has the most bass if you like that, but it's not as clear or "hi-fi" sounding as 797/49990. I already had the browndog adapters so i only had to buy the 49990's, cost me 15$ for 2 of them shipped(DigiKey). I've seen them on ebay for 20$ for a pair soldered to an adapter, but it's ebay so who knows how legit it is.
You can buy a pair, already soldered to an adapter @ browndog for 33.00 + shipping, which I think is a bit high, if you have the means to solder them yourself.
Edited by MikeW - 1/16/12 at 1:29pm