Injecting one sub to Benchmark system…

I was in this situation in about 2006 with a dac1 and a sub.  The new models may be different but I thought back then that I really lost something by having the DAC output going to both an amplifier and a sub.  I'd at least experiment with getting an adapter and running the sub from the headphone out.  I eventually got a regular preamp and I thought that was a substantial improvement in definition through most of the frequency spectrum.  I'd also experiment going power amp to sub because that definitely won't take away from the low level signal that is easy to mess up.  

I think the time has arrived for people to experiment with cheap performance oriented electronics.  I've recently bought a couple of <$150 Schiit products and they're great.  At work I have a Fiio x7 to Schiit Magni+ powering DCA Aeon Noires and it's great.  Nothing about that setup bothers me and I'm pretty easily bothered.  If a preamp died on me I would not hesitate to try a $599 Freya S.  

The idea behind running the headphone out for the sub is that having the pre-outs running two sets of wires at the same time and into 2 amplifiers at the same time is harder for the dac to power than a single set of wires and amp.  Running from the headphone amp to the sub would, I think, reduce that because the headphone amp is its own separate amplification from the preouts.  And it's something you can try for the cost of a $5 headphone jack to rca adapter.  

IMO it's a mistake to not try a regular preamp with the Benchmarks.  While there may be a tiny loss of transparency I found a preamp was overall a pretty big improvement.