let me butt in here...it was said that the jb3 takes optical in just like dat...optical is somewhat uncommon in dat recorders...true they make a 7-pin optical but the majority of folks seem to use coax instead.
secondly, to help clarify what skalinder and hurley said...the mixpad only provides analog outs...it does not convert the signal to digital. there are some pre-amps that have that feature (ADC) included, such as the v3. you do not *have* to use an ADC to convert the signal before recording it, however it is highly recommended with the jb3 because of the low quality of it's analog-ins (and subsequently its shitty built-in ADC).
to maximize the quality of your recordings with whatever gear you choose > jb3, get a separate ADC.
that will mean though that you're going to spend more money...probably a few hundred more than you were planning to with the current rig you've mentioned.
of course, these are just some more things to think about, ultimately you'll want to base your decision on what your own ears tell you and what your wallet can handle. you may not be able to put together the ideal rig right away, but be sure you have done your homework before you start buying stuff. listen to plenty of tapes, learn about each piece of gear and why you'd want/need it, factor in all the accessories like battery power/cables/stand/mounts/bag that you'll need...
i did some research before putting together my rig but i wasn't at all involved in the taping community, this site wasn't even around yet, and i might have made some different choices had i had all these great resources. not to say i'm not happy with my tapes, i've pulled some great ones, but i certainly didn't know of all the different options there were available to me!