Seth=L said:
The fronts go lower than the sub? Maybe get an SVS.
Agreed. I have never heard of this Soundstage brand. There is a guy selling JBL E20 bookshelves for cheap (got mine for $73 shipped) and they are factory refurbs with the warranty. I would recommend them as rears. I don't think you will be too messed up going with different rears, just get something with a similar sound as your fronts. I was running some Bose cubes (got them free) for fronts and rears with a HUGE wharfedale opal center. The center beasted the cubes. Now I am running the wharfedale as center, the E20s a fronts, and cubes as rears. It is my g/fs system and it doesn't sound bad. The placement of everything is bad, and we aren't worried about it till she moves.
For my system I will be running my 20's as mains, the wharfedale center, and probably some E30s as rears. Maybe get a PB10 for a sub, but not while I am in an apt.
Unless you are a HUGE audiophile, just get good quality pieces that sound similar and you should be ok.