In the effects send/return you can wire a pot in a box so you can crank the pre-amp and the power amp part will not be driven to full volume.
Or plug in "attenuator cable" aka "padded cable" aka "dubbing cable" - this will do the same but usually at a calibrated db level.
and/or wire in one of these
STEWMAC.COM : Black Ice Overdrive
Once you figure out what you like you can commit to hardware changes.