I use a variation of your system, for the same reasons, the difference is I use an amp and cab, too, for the drummer or guitarist to hear if/when they're not using IEMs.
I run the Tuner out of my Markbass F1 into one channel of a Behringer (I know, but there's a better control over levels) HA4700, and the aux send from the PA into the other channel, and I can get a good mix of me and the PA send into my IEMs, with even some rudimentary EQ. It's never crapped out on me yet, and is even fairly quiet (certainly quiet enough for use live). The DI to the PA goes from the F1, which separates it from the signal levels for my monitoring.
I should add that my signal's already wet before it hits the F1 (which I run flat) as I use an iPod-based preamp (the Jampup modelling app).
Dunno whether that helps, but it certainly works for me.