I just wrote a reply to this basic question today via e-mail so I'll paste in in here:
While it is rather easy to put both RCA and xlr connections on the unit I am strugling a bit with finding a really good way to implement mixed signals. On the old TVC a lot of work went into getting it to 'convert' from rca to bal and bal to rca. Not easy but worked out pretty well when we were done.... With autoformers (by virtue of thier design) they will not ever 'convert' like that.... It's easy to make a bal unit and then add rca connections into the mix - just faking out grounds, etc to make the system work fine. I have mixed feelings about doing the mixed bal/rca units unless they really do convert signals- since folks expect that if the plug in bal and go out rca - for example - that it is making full use of that bal input. Also the cost of the fully bal TAP-X would be pushing $3K and that is getting up there. Because of all that I decided to get this stuff rolling RCA only (or single input XLR) and then re-visit the mixed connections thing this fall when I get some clear head time.....
That kinda sums up where I am at with it! Any feedback on folks priorities would be great.