connecting a sub to a 2-channel system


My sister is coming for a visit. she is a budding audiophile and we will be having a listening session in front of my 2-channel rig. She is still very much a bass-head, and I want to hook my HSU VTF MkII sub into my 2-channel system, so I can show her what it sounds like with and without the big-booty-bass. My question is this: how to best hook the sub into the 2-channel system? My current thinking is to use a Y-adapter on a single channel coming out of either the pre or the DAC, then use the Audioquest sub-x cable to the HSU's LFE input. one channel from the DAC would be fixed, using a single channel from the pre would be variable. Thoughts? Thanks in advance. Keep in mind this is not a permanent addition...!
realremo
If the HSU has speaker inputs, you can use to speaker taps from your amp. I find this to be an easier blend since sub and speakers see the same signal. It's how mine is hooked up.
I think that's how I hooked up the HSU to my Yami receiver back in "the day" (2009). The Yamaha had A/B speaker connections tho, the Rotel does not, so I'd have to wire both sets of speaker cable (quad 22l2s and the sub) into the same single pair of amp connections? I think that's possible, was planning on "dual wiring" the quads anyway. I use Audioquest type 4 cable, and there is still room inside the AQ bannana plugs for another twist of copper, but I would have to get longer runs of wire for the sub, which will go in the corner. You don't think the Y adapter trick would work?
I'm not a "y" adapter fan, but in some cases they work without sonic degrading.