You think itd be overkill to add an m13 beside an x3/xtlive?
Not in my book it aint. As you can see IMHO the technology that Line 6 use now is based on the X3's processing power. Its all about the X3 (sorry XT). Let me drive it to this.
Since the POD is almost a whole band arsenal the processing power is limited. The POD's PP is focused too much on the AMP SIMULATIONS rather than the EFFECTS esp on the DRIVES w/c the DRIVES are lacking so much.
Then there's the M series (M13/9) comes in. The PP focuses on the effects alone so it may give you a tonal advantage over the POD, but no amp sims. (They all counts digitally.)
Some people pair up the M series to other amp sims like Sansamp Liverpool.
So therefore putting the two together.
POD (awesome amp sims) + M13/9 (awesome effects) = pawnage tone
To pick between the two? I'd really go for the POD since its more "multi" than the M series.
POD... you all have it in a single black box. lol