It will depend on the speakers, and the best may be to emulate your speaker manufacturer's own subwoofer crossover setting.
Otherwise it looks fine to me. On your screenshot it's not possible to see what you are sending from you DAW's LFE output on the middle row. In a cinema setting the LFE would be calibrated +10dB (as far as I can remember!), so if you're using your subwoofer for both bass management as well as reproducing the LFE channel you'd need to at 10dB to your middle row LFE output (or reduce the bass management sends by 10db)
In general, while it would be brilliant to have dedicated surround support on TotalMix, I don't really mind the situation we have now. It's completely flexible, with all the bussing. I'd be worried with dedicated surround we'd be locked into some set ways to do it.
Set up differ so much. Some use bass management, some don't. I use a hybrid, as ATC recommend their subwoofers to work in addition to the mains, and not filter the mains, etc. If RME do implement surround they'd have to keep it open enough to accommodate a wide variety of surround formats and speaker systems.