FET amp emulations in front of a solid state amp

[marino]

Did anyone of you noticed problems when attaching distortion pedal in front of a solid state amp. That includes FET emulations from Runoffgroove. In a way that the sound is very harsh, painfully bad in upper freq, just as bad as original amp distortion on dirty channel. By the way I'm using Marshall G30 RCD with decent clean and overdrive channel to forget.
I know my pedals are ok, cause when I put opamp amp emulator sansamp GT2 between amp and FET pedal, it works.  Infact GT2 is only thing that works as a distortion through clean channel.
Maybe some kind of a buffer would solve this. Or cabinet simulator?
If someone had similar problems, I'd like to hear your opinions.

Thanks

Marin

[javacody]

I have a 64 Gibson Skylark with a Jensen Reissue 10" speaker. Jensen speakers have a higher frequency response (I think this is the correct term?) than most guitar speakers and most FET based OD's/Distortions sound raspy and fizzy through this amp. I've been wondering if I could eliminate a lot of this fizziness through either a marshall cab sim into the amp or by using an EQ pedal?