I'm far from an electronics expert, so I can't answer to the ins and outs of splitting it.
However, when I first bought the -10 there was an issue with the RS-232 feed to my Digiflight II, and after some research and discussion I split the feed just like you mentioned.
It worked just fine.
That's my "n" of 1, FWIW.
KUMP - Indianapolis, IN
RV-10 N316JS bought / flying
RV-8 wings / fuse in progress ... still
N329TS (had it, lost it, looking for new number)