Signal routing without a mixer

[Mark Hamburg <mark_hamburg@baymoon.com>]

If I don't end up going completely minimalist, I'd at least like to figure
out how to run my little looping rig without a mixer if for no other reason
than to avoid having yet one more thing that wants power.

What that seems to require is something that will take a stereo signal,
split it into two left/right pairs, and sum one of those pairs to feed the
EDP. I can combine the signals again at my EQKiller.

Matthias covered some of this recently in the ABY etc. discussion but he
also seemed to suggest that at the very least one needs hard wired 
resistors
to get appropriate signal mixing.

What are the consequences of splitting signals using Y cables?

What are the consequences of mixing signals using Y cables?

How important are those resistors?

Thanks.
Mark

P.S. This does highlight the one nice thing about the Jamman relative to 
the
EDP: It was a mono-looper, but it was friendly toward a stereo signal path.
Or so I've been told.