As a starting point, I tend to match, cost wise, component to component since performance to cost ratio tend to be similar. Since the 41- cost me $209, I pretty much decided to start looking at a sub in a comparable price range. Matching a $209 bookshelf to a $700+ sub isn't something I would do unless there is a compelling reason.
A good reason is that this speaker is
not a $200 bookshelf. It's a $1000 MSRP bookshelf, and could easily sell for two-times that, still in my opinion . That's not just lip service. The EMP E5Bi is an ACTUAL $200 bookshelf (actually, it's $250/pr). The E41-B is probably twice as resolving with a more liquid midrange and much more HF definition and "snap" - and given the logarithmic law of diminishing returns, EMP is probably crazy selling these things at $500/pr. The only reason they can get away with this is probably because they make more volume on these when selling the aluminum ones to dealers. So what you're paying for the I.D. ones is probably dealer-cost.
While I don't know what percent of the cone makeup is beryllium, the fact that they attempt to use the material at all is astounding. The midrange resolution you get from these speakers in the nearfield may just be as good as any other setup.
You'd in my opinion be reducing the fidelity of your system with a cheap sub like that rather than increase it. These speakers want a very good sub.. or three. Else don't bother with a sub at all. I don't think the speakers sound poor at all without a sub.
Now if you can get a true $1000 sub for $200, that's totally different.
For my E41-Bs, if I get around to it, I want to pick up one of these:
http://www.amazon.com/SWR-823D-Alpine-Type-R-2-Ohm-Subwoofer/dp/B0056VZ6YI
They have a very nice BL curve and extremely low inductance, and decent extension too. My guess is this driver can run with $300 scanspeak etc units even as a woofer.
Gene's upgrade of the tweeter makes the speaker match to the MiniVee a little more logical.
The actual tweeter on the E41s is still excellent. KEW for example said it is one of the best soft domes he's heard and - unlike most soft tweeters.