Mike,
There is no reason you can't use EF30Cs for front speakers but I highly recommend you consider the two hottest deals on EMP speakers offered right now as they are bigger bang for your buck.
EF30T 5.1 system for $899
http://store.audioholics.com/product/1831/1/emp-ef30t-5-1-speaker-system
and the EF50T 7.1 system for $1099
http://store.audioholics.com/product/1833/1/emp-ef50t-7-1-speaker-system
If you can swing towers for the front channels, this is one smoking deal at more than 50% off that will expire at the end of May. Tom Andry reviewed both the EF50T and EF30T and found them to be excellent performers, especially the EF30T which beat out his former reference speakers and he now uses instead.
With the savings from these systems, you can put towards an extra E10s subwoofer. You should do your best to get 2 identically matched subs as two subs properly placed and setup are always better than one sub to yield more even bass distribution for all seats.
Alternatively if you hold off till summer, Emotiva will have a killer subwoofer system consisting of 2 12" sealed subs and a 1000 watt amp for around $1k. Their speaker system is also excellent and easy to install into cabinetry or on walls. We have a formal review on the ERM 5.0 system you should check out.
Consider your space limitations and how you will install the speakers before settling on a system but try your best to integrate 2 subs if you can using the guidelines I outlined here:
http://www.audioholics.com/tweaks/get-good-bass/subwoofer-connection-guide