Personal IEM transmitter/transmixer as a DI box?
 

http://cdn.shure.com/product/main_im..._img_p2t_l.jpg http://www.sweetwater.com/images/clo...H2_detail4.jpg
http://www.rolls.com/images/productImg/PM351_Large.jpg

I just recently converted to the world of in-ear monitors (IEMs) and noticed that most systems provide a mixer before the signal is sent to the main FOH mixer board. The pictures above of the Shure P2T and the Rolls PM351 are examples that show inputs for a mic and an instrument. In both these systems, the corresponding outputs are balanced XLR signals.

My questions are:
1. Can these systems replace your DI box?
2. Does anyone use this configuration and have any opinions on their experience?