I will say that I believe IRs make the 11R a top shelf unit. In fact, they will also make something even less expensive sound awesome!

To spare you the boring details - I use a Digitech RP360XP -> Torpedo CAB -> Line 6 M9 -> PA rig at church. Using the Scumback Ownhammer IR lights the Digitech preamps up!!! In fact, the CAB lastest firmware update puts their native cabs on par with the Ownhammer IRs (IMHO - although I admittedly don't have fool-proof ears when it comes to this sort of stuff).

Not to derail off the EPSi - but more to confirm that a quality IR loader will transform your tone.

Although I am in IT professionally (I am in QA currently although I did spend some time as an application developer) I can't say I know the details on DSP usage. What I hear over and over is what TLTD stated above - IRs seem to take a ton of resource capacity. To find a unit that does only that allows you to get top shelf quality without having to pay another $1K or more to get it.

To bring this long winded post to conclusion - although I am using a Torpedo CAB I would go out now and get an EPSi today if I didn't have the CAB. It makes THAT much difference (IMHO).