As far as I know, that is MADE for those types of mics. It will actually benefit from that power and handle higher spls. It does not take any power from the MT, just 12v from the dongle. However, you will lose the bass roll-off. I would recommend getting the battery box instead. If you get the modded sp-spsb-6, it'll be just about the same size as the dongle, and the roll-off is almost required for these mics as far as I know. Also, yes... both of those do not take any power from the MT, only the MIC one I pointed out does. If anyone else has any experience, fell free to chime in.
So. I would do one of two things if I had to choose.
The exact setup you have up there already, except using the modded sp-spsb-6 box to cut down on some size.
Or...
Using this SP MT interface,
http://www.soundprofessionals.com/cgi-bin/gold/item/SP-MICROTRACK-INTERFACE . All this one does is just convert the 1/8 to 1/4. So, it replaces this thing you have
http://www.soundprofessionals.com/cgi-bin/gold/item/SP-MICROTRACK-MINI-TRS . But it's smaller and cuts down on size, as it's shaped in a easier way to deal with. (In my opinion). Then just add everything else, and the modded sp-spsb-6 battery box. That is probably the smallest solution to me with that setup. I like my stuff as easy to deal with as possible, for when setting up in a stealth situation, it cuts down on time needed.
Those are just some suggestions... The stuff I suggested is just small things that you may or may not care about, you can figure out what works best for you with that hopefully.
If you have any other questions, call soundpros personally and ask for Chris. He will help you with EVERYTHING for planning out your rig and can do any special requests you may have. Seriously, he is an awesome guy to talk to and definitely knows his stuff. Say you're from taperssection and he'll give the discount over the phone.