I'm also wondering about this.
jam apogee
This product seems more high end but $100 . . . pricey
iRig looked ok. I think the headphone jack on the ipad also has input capabilities if I heard right.
I don't think radio shack could make a thing like iRig because the iRig 1/8 input is both an in and out? Is that possible?
I don't seem how else the iRig thing could work then have the 1/8 input also being an output because there isn't another out on the ipad right?
The Jam USB looks good but maybe could look for other 1/4 to USB converters?
Does Jam meet certain specs that a regular 1/4 to USB converter wouldn't?
thanks