looping different instruments and voice

[Scott Stroud <scotty@numericable.fr>]

Hello

Due to budget issues, I've been stuck with looping guitar or banjo  
licks on my Akai HeadRush , then pulling out the in- jack (luckily  
with no apparent noise) and putting in my mic jack , to sing  
different layers on top of the existing loop. I'm now ready to get a  
bit more complex, and am considering the Boss RC-20, the Digitech  
Jamman, or the new Boss RC-50.

These all have different inputs I believe, can they be used together?  
I wouldn't need to loop more than one input at a time, but how do you  
switch without using your hands? Like say I put down a guitar loop,  
want to add some weird keyboard sounds, and then sing over it all,  
and put on my own harmonies. Can one pedal do this?

And can the RC-50 loop itself, like the second track looping a part  
of the first, etc?


Cheers for any info

scott