EXS 24 Logic Sampler Users Group

I would actually keep both, that way you have both the virtual world 
and hardware world at your fingertips. What might be funky is to 
replace the E4 with Emu's new E5 soft sampler, apparently due for 
release in Jan at NAMM.
Also, bear in mind that Emu have a vast library support and third 
party libraries are available everywhere.
I have both, simply because I am a Sound Font developer for Emu and 
have made a number of their soundsets for their modules and command 
stations, and I use both. I love the EXS24 Mk11 and have created a cd 
rom for that also which is awaiting endorsement from Emagic. I can 
honestly say that I use both and would not part with either. I love 
the interface for the EXS and find it easy to use but I love the 
power of the E4 in it's modulation matrix and filters, this EXS 
doesn't have.
If you can, try to keep both.
Best of luck.

http://www.samplecraze.com