Just would have loved to hear back from someone who actually did it (or a very similar setup)
There are a few testimonies here and there, but they are sparse. My case use is probably be the same (PC or radio receiver -> Topping Dac/Preamp [so it can auto/on off and trigger on/off the power amp]->Rca to active subwoofer ; XLR to Power amp ->speakers).
I think it could be done with the E70, E70 velvet, D70 pro (Octo and Ess versions), the DX7Pro+ and the Dx9 (at least, I might miss some - must write down somewhere which ones have simultaneous RCA&XLR out, auto-on off and 12v trigger out) ; but it's way too late here for me to have the concentration to compare specs, functions and measurements to see if what's worth between going 400 (E70) to 1300 (Dx9) bucks and everything in between