I use the Atomic reactor FR with my X3L and am fully satisfied with it for my needs of power and so on (the Atomic that is, not the entire rig) after having tested it at rehearsal and on stage a few times. I also have a Fender hot rod deluxe tube amp with analog pedals to compare to (I believe the Fender can play louder than the Atomic, but haven´t tested that really).

But I had a problem with the sound being "trashy" or "phasey" or something like that. It didn´t really sound good, especially when played together with other instruments. Or it became more obvious then.

I have been discussing this issue in another thread here. And the conclusion is that it is propably because of the mic simulations. They should be turned off when the X3L is connected to the Atomic FR or other fullrange amp, to get the "amp in the room" sound and feel. The problem is that the only way to turn off mic sims is to also turn off cab-sims! Which means the sound output to a fullrange system like the Atomic FR will be wrong.

There is the solution: sell the X3L and get a Vetta instead... I don´t want to do that.

After doing a lot of research, believe it or not what worked the best for me was incredibly inexpensive. I run two Monster XLR cables out of the direct outs on the back of my X3L into two 150 watt Harbinger APS12 powered speakers and it sounds fricking incredible. Total cost of $350.00 + a little tax and thats all you should ever need. If you need larger, that venue WILL have a more powerful house system you can plug your X3 into and then just use one (or both I guess) of your speakers for a stage moniter. Check it out for yourself, I personally don't notice nearly enough sonic difference from the Atomics to make that much of a price jump justifiable and I am a total sound nazi. If you don't like them, you can always just return them before the satisfaction guarentee runs out.

You are still using cab sims though, right? In theory, you should turn those off as well when using an amp or stack setup. The guitar voiced speakers already equipped will screw with your tone and make it sound kinda trashy is what I would call it as well. It really depends on what your connecting to really as to how much control you really want in this area. For anything that involves a PA, I would definetley be using the cab and mic sims (I always turn all the room off on the mics, if I want "room noise" I just use reverb instead.) But then if you were going direct out to the house PA but using a guitar amp for a stage moniter, things would be different. I couldn't pull it off actually because my tone is based on blending two amps together, so no dual tone to save me either in this situation. That, my friends is the reason I choose to go with powered speakers before anything else. Consistancy is so very priceless.

For those powered speakers you had that didnt sound good without a mixer involved - Is there an input level or trim setting you can use on these powered speakers somewhere? Technically Line 6 says you should have that set as low as possible and the master volume on the X3 should be maxed for best sound ratio. From what you described anyways, I would guess that the mixer was trimming off some of your sound for you but this just got overlooked on the powered speakers and was set to high. Sometimes I forget to think about that stuff and am left going why the hell isnt this sounding right? and then have one of those I'm an idiot moments, we all do it once in a while, come on now. Hope that helps!