Encoding 4 channels in 2 tracks. is it possible?

[Freddo30]

I have this stereo unit that i love for mobile
recording, and im having a hard time moving
to something else.

I decided long ago that i wanted to keep my rig
the way it was, and see if i could push things
A little farther.

so i started recording 3 channels with an
external mixer, using lef, right, center and
then doing the channel separation in post.
It works great and love the results i get.

My question is:
can i do this with 4 channes?
Is it possible to somehow send 4ch in the stereo
track and then separate them in post?

[MIKEHARRIS]

is it an analog or digital recorder ?
If analog...no...if digital yes...but you must have an AES input. Dolby E permits up to 8 channels to be recorded on a AES pair. Very expensive

It might be better to look at the new crop of multichannel field recorders...from Tascam..Zaxcom or Sound Devices. Those seem the most professional.
There may be some budget stuff from folks like Zoom

[DaVogi]

it can be done in analog but only with artifacts and limits (just look at the analog dolby matrix-systems like pro logic and dolby surround)... you don't want this for recording or music.

[Freddo30]

is a regular USB interface with only 2 analog inputs.
Spdif input also available. Mbox style, but chinese.

I do get a little bleeding from time to time with left
And right channels, but compared to a headphone
bleeding on a vocal track is nothing.

Some dolby units ive found are 16bit only.

Any other ideas?