Luckily DSL's are master volumes AND have an FX loop. Get the DSL halfstack
and an Alesis Nanoverb. Put the Nanoverb in the loop, then turn the amp up to the same level you'd use it in a rehearsal room. Set the input to a proper level, mix your reverb to taste, then use the output knob as your main volume. It may not be exactly like using a THD Hotplate (another option), but you'll be pleasantly surprised to see how cranked your amp sounds at practice amp levels. Plus the reverb will make you feel like you're at Madison Square Garden.....in your bedroom!
Any FX unit with input, mix, and output will work. The Alesis sounds pretty good, and you can get them for $60 used.