Combine two "mono" miniSHARC or SPDIF outputs

Hi folks,

a seemingly wild idea:

to maximise the number of available FIR TAPs I had the idea to run two miniSHARC (or two openDRCs) in parallel, but only use use the left channel in device 1 and only the right channel in device 2.

My question: How can I get the device 1 left output and the device 2 right output combined back into one Stereo SPDIF signal in hardware (without using a PC or mixer!)?

Thanks and Regards,
Winfried