I'm not an expert here, but you may need to change out one of the two units to make this all work. The Burl is RCA only, so that one must connect the the RCA SPDIF input of the 002. The UA has an optical out, but the question is; can the 002 use SPDIF on both RCA and optical at the same time? In any case, both units are 2-channel only(which may be fine for your needs) and you will NEED to find a way to clock everything so you don't get clicks and pops on the digital sources. My instincts suggest, the Burl as the master. Set Pro tools clock source to the SPDIF RCA(so it slaves to the Burl). Feed wordclock from the Burl to the UA and set the UA to External clock.
Just my 2 cents, but it seems to me that changing out your output path when you need the extra inputs would be a PITA, so I would look for another way around and add a dedicated lightpipe device(leaving the UA as your output D>A). Considering the possibility that the lightpipe is stuck in ADAT(8 channel) mode(because RCA SPDIF is already being used), there are several 8-channel options, such as:
1-Behringer ADA8200(the red one) that has line inputs(for your Great River preamps) and is really a solid performer for cheap(and can be upgraded by BLA)
2-Midas XL-48(which has become my "go to" for drum mic'ing)
Food for thought
