I didn't measure all those things. I did run and record the same vocal, bass, and drum takes through the unit before and after and observed an eq analyzer and listened. Before and after I ran 1k through it and measured the voltage to make sure db was the same. I didn't think to save the audiophiles, I was doing it for me.
I did not re-bias the tubes. They're the same tube type. I kept the original EL84, I believe that is the only tube that would need to be biased. I may be wrong.
For all I know the poly's are good caps. They're yellow ones of which I've never seen before, but I already had that value of WIMA's lying around. The Jamicon's are pretty terrible in my experience and I was surprised to see them in there as I've only seen them in 80's and 90's toy keyboards. Doesn't mean that these particular Jamicon's are necessarily bad, considering I don't have experience with modern ones. These may have been selected for low impedance. Who knows?
All I have to say is based on my limited testing, It thickened my audio signal. Maybe it was just my unit, but what was coming in was coming out noticeably thinner in the low end, even after the tube change. I'm happy with it now.
I changed out the yellow poly's as I already had those value caps (0.1uf and 0.01uf). I also changed out all the electrolytics in the signal path on main board with the tubes. It was really easy and cost me no more than $10.
I'm going to change out the big 10uf film cap and see if I notice any change. This time I'll level match and record some audio. If it seems to me worthwhile I'll post about it.