If you're already recording on your laptop, why not just get an interface that can handle 4 channels or more (and then do it all in post)? A lot cheaper than an R4.
VX Pocket 440
Presonus Firebox
Come to mind immediately. I just picked up a Firebox to mess around with in fact. 6 channels simultaneously (2 mic, 2 line, 2 digital) - might be a pretty cool thing!