As the OP said in his opening statement:
"As you can notice I do not have an unlimited budget but I think either of these options could give me what I am looking for."
Given the upgrade in speakers was around $500 and the EP125 is around $500, I figured he had about $500 give or take maybe $100. Not $800.
which is why I said, if you can gather an extra $100 go for the EP175. I think most people think the EP125 is only good for closets.
I had a EP125 quite a few years ago and was surprised actually just how better it was than one might think. So, what it is an 8" driver.
For $500 it is not that bad, if your not into watching movies at a above avg volumn. It will give the M22 more bass. I would not want to turn it up, though. If you watching tv or listening to music at say a person does at a volumn level when speaking then hell yeh, it will surfice, a EP175 wouod be better. And yeh, heck A EP350 would be greatly improved. I don't know about the EP400 as most will say it's only a 8" driver. But as far as I am concerned an normal guy That EP400 would sound awesome.
Why the heack would Kreisel, who is the man that invented Satelite/SUb combos use a dual 8" driver in his new line up if it wasn't good. M&K speakers !! used in alot of mixing studios for music and movies as reference speakers when doing sound. I would think he knows a bit about subs.
Another and although the use 3 - 8" drivers and have rave reviews is Paradigm and Martin Logan Depth subs.
I would think if you not going to be raising the volumn higher than maybe th db lev of some one shouting the Ep125 givin your sitting at probably 10 ft away will give the bass you need, the EP175 would be an improvment. The EP350 well look at it, but I don't think you are planning on spending $900 by the time you add taxes. And pretty well sure $1500 on a EP400 is out of the talk, if not may as well go with the EP500 at the same cost.
anyways, my two cents worth ... it is easy to say get the EP350 with some one else's money. Heck I want a EP800 and two EP500 for my 11x21 room, but probably wouldn't notice the difference with two EP500
M80 HG Cherry
2x Energy ESW10 Subs