DIY Valve preamp into Solid Sate Power Amp (Help!)

[sonoman1979]

Hi, I just build a jcm 800 preamp (see the image) with an added gain satage and some mods based on recomendations to get AFD sound of Slash. I know that I won't get the same sound without the tube power amp, but I just want to get a decent sound. In this case I'm using my Randall RG100SC_G2(all solid state)'s power amp, connecting the valve preamp to the "return" connector (effects loop) of the randall. I like the sound, but If I compare it with the real ones (AFD all valve mods), it seem that I'm loosing a lot of hi frequency. I tried modifiying the preamp and get some results, but I want to know if it is posible to modify the negative feedback (that I think the randall shoud have) and get the sound improved. I don't have the schematics of my randall but I think that should be similar to the RG100ES (see the image).
Another thing, when I connect an ipod in the return of my randall, I also get a poor sound, with hi frequencies cutted.
Excuse me for my bad english.
Thanks in advance.