While my new Amplifi 150 is in the shop (power issues?), I took the plunge and bought a CRATE powerblock to use with my trusty Pod XTLive board - and used the Crate powerblock only as a power amp into my Fender 4x12 cabinet. It worked like a champ.
You do need to configure the OUTPUT setting on the Line 6 Pod XT LIVE (I chose power amp, not direct) - but that's usually the case.
Guitar into Line 6 Pod XT Live
Line 6 Pod left + right outputs --> Crate Powerblock LINE IN (L&R)
Crate Powerblock L&R outputs ---> Cabinet (The Fender 4x12 mustang cabinet can be configured to be stereo)
You can see in the picture, pretty easy setup.
Note: during a live show, I always use my Boss Tuner (just used to it I guess) and I had bought the Behringer Ultra Shifter/Harmonist US600 Processor pedal so I easily drop to an Eb if needed. Versatile little pedal.
(and yes, that's a Kramer 5150 replica, which I use for the fun Van Halen party tunes at the end of the night - always fun to play and usually a few guitiarists in the crowd appreciate it.)
Crate powerblock was $100 on Craigslist
I've previously used the Pod XT live into a Roland Keyboard amp (KB300) but it's very bass-y. And it's only 1 speaker (albeit powerful). Having a 4x12 was helpful as it filled the stage (an outside benefit show).
I spent a lot of time pondering the FRFR (Full Range, Flat Response) route - but this was just as powerful, much more affordable, and flexible. Plus, the stereo effects were nice to hear on stage.
Hope this helps someone pondering power-amps in a live situation (like me a few weeks ago).