Can't say if it sounds good as I haven't even heard the e1010i yet lol. I hate talking about it haha. I want both of mine now!! I didn't hear that 4 e1010i setup either. Obviously it's not hitting sub 25hz content with ease, but I bet it sounded damn good on 95% of movies and all music. It seems every review I've seen about the e1010i where the listener has heard other quality subs in the same room (same time a few times also; hsu, svs, dayton, etc etc) has had nothing but good things to say about it's sound quality.
Adding more subs won't extend you any deeper really. Maybe a hair, but not much. If you have any nulls or anything like that that could be hurting your lower end also. The only way to get some serious sub-30/sub-25hz content is to go to a different sub. Cone area, power, large enclosure/infinite baffle (unless there is some serious eq applied like the JL subs). Of course...that comes at a much higher costs. Many recommend the pb-1000 at $500 as that will dig down into the lower 20's easily, but likely not with a lot of volume. The next steps up are LFM-1ex/PSA xv15/etc at about $650+. This is just one of those points where you have to ask yourself is it work the extra money to have that content or not. Obviously everyone would love to, but many different factors play into everyone's final decisions.
