I have a Humminbird SI unit on my console with the split transducers (one in hull and one transom mount), I'm putting another unit (lowrance) on my console with the bird and am going with the in hull transducer. What issues and hopefully solutions to them will I run into. I know the main one will be interference from the 2 in hull transducers being side by side. Anyone have this setup and make it work??

Hmmmm, just curious; but why? I'd suggest you contact Member Wayne P in the hummingbird page here before you make a mess and throw away money.

wanted a dual setup to dedicate each for a specific purpose....(one SI and other sonar/down imaging). I know if one is just GPS there would be no problem.

I think (keyword) the problem will be because the hummingbird uses 83/200 sonar with its side imaging, as a combination. The new touch lowrance graphs also used 2d & sonar at the same time. Here's where the problem comes in, you could select 200 on the lowrance and 83 on the bird and have no issue; but the bird won't let you do that! It uses 83/200 all the time, so you can't avoid the interference at all.

This is why I said contact Wayne, he's a bird guru and could be the one to confirm it.