I find when running a pre into an amp it helps to keep the amp volume low initially, and crank the pre volume as loud as you can while still getting minimal noise from it. Then raise the amp volume to a reasonable level.
Something about running a pre into a combo amp with another pre raises the volume and noise floor a lot. But IME by playing with the volume levels you can get a loud signal with minimal noise.
I run my pre into a boss ME-50 to split the signal into a mixer or amp, and when going into an amp it can be very noisy unless I keep the ME-50/amps's volume very low (like 20-30%) and crank the preamp volume. But going into a mixer is fine, probably because I use a passive mixer so the signal isn't going through a second preamp + a power amp. With a mixer I can keep the ME-50's volume around 50-75% without it getting too noisy.
Amps with preamp in/out jacks could help, that way you could run any preamp instead of the built in one. That would likely fix any noise issues caused by running 2 pre amps.