First off let me say, "Yes, a tube amp."
I assume you were using POD HD amp sims when running direct and getting that gritty and nasty tone that didn't sound at all like what you spent time tweaking in, right? The problem was not the amp sims but the direct out to PA. Without an awesome sound engineer that cares what YOUR tone sounds like, it hopeless for that to sound too amazing.
I think the best solution for ultimate flexibility without buying a DT50, is using POD HD amp sims or amp pre sims with the 1/4" outputs hooked to the FX Return of your tube amp. Set the "AMP/LINE" switch to "LINE". Also, set the output mode to COMBO PWR AMP. Now you can use the patches you had and tweak them to sound good with the power tubes of your amp.
You can play around with the full amp sims vs. the amp pre models, and see which sounds best for you. Also, you may or may not want to use the cab sims, since you'll have a real one. But it does work when wanting to make your 1x12 or whatever sound more like a 4x12, or just plain different than it really is.
I've done the four cable method, actually 7 cable because I ran it stereo. I always ended up with noise issues one way or another. So went back to POD amp sims to analog tube amp FX return. I can control my levels much easier in the POD than walking to my amp and taking my hands off my guitar to turn a knob.
I use a Bugera 22W for my second channel right now. My first channel is a Crate Vintage 50W. So I Have EL34s on both power amps. So I can combine any of the POD HD amp pre models with my EL34s to make them sound Fenderish, Marshallish, Voxish, whatever. I can also choose to use the full amp sim (including power amp sim) when trying to make those EL34s sound different than they really are, KT66s , 6L6s, what have you. Kind of the same as the cab sims.
Always tweak your tones on what ever you'll be using them on (e.g. tube amp, headphones, PA), or they won't sound the same even if you change the output mode from Studio Direct to AMP Front or PWR it can't fix everything. By tweaking in the environment you'll be monitoring by while playing is I think the best route.
Hope this was helpful.
