If it were me, I'd buy the best I can afford piece by piece if necessary. I wouldn't buy a small sub knowing that I'll replace it in a couple(?) yrs down the road with a more powerfull one...to me that's kind of wasting money, just my opinion of course. The EP350 is in a different league than the 125 and there are also a lot of other co's out there that make excellent subs too.
If you have room for a bigger sub, and you can afford it...I'd go for it since you want to set up an HT down the road anyway. Why not try out the M22's by themselves first? though they do benefit from a sub, maybe they'll be enough to get your feet wet initially.
