I just did that, sold my Marshall half-stack and bought an amplified PA speaker.
I don't have the Line6 pedal you just mentioned, but I will be getting it when my budget permits it.
For now, I'm using a Digitech RP-500 guitar effects unit (which has amp and effect modeling). The output of the RP-550 goes to a mixer, and the output of mixer goes to the speaker. You don't really need the mixer, you can plug straight into the speaker, but I also sing and plug other stuff.
I loved the sound of the Marshall, but the only problem is that not all effects sounded good plugged into the front of the amp. Some sounded a lot better through the effects loop. Plus, as you said, the amp itself colored the sound.
With it plugged into a PA speaker, I get the true sound coming out of effects unit, and my sound was never better! True that my Marshall had a sweet sound, especially for blues.. But changing sounds on the fly was a pain at best to impossible at worst.
I have a host of presets programmed into my pedal, and all I have to remember is which preset is for what number. One less thing for me to worry about on stage.
So Tx, in a nutshell, I'm very happy with my sound/ Wish I had done this sooner.
Next step is to buy 2 more speakers as my main speaker (using the one I have now as a monitor). This way, no matter where I play, I don't have to worry about adjusting their PA to your liking. I will have my own sound no matter where I go.
Good luck,
Itchin' to play,
Izzy