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
I'll try it tomorrow night with the sub turned off, see if that restores the Quads' ruler-flat mid-range. I feel like I am missing some detail in the mids, like the sub is covering it up or something. This is only temporary anyway, I miss the sub in my home theater too much! Funny how I used to crave bass when I first got into this hobby, now I just...don't!
I think I know what was wrong, crossover was not set correctly, now the sub and speakers overlap pretty seamlessly. Thanks all.
OK now that my sister has left, her visit ended, I returned the sub to the home theater system for our viewing of "snow white and the huntsman." I listened to my 2-channel system for about 2 hours last night and I think I miss the sub. It added some weight and presence to the music. Another thing: I use a computer desk in my listening room to work from home, I just move it out when people come in for a listen. I had to move it back in last night. There is a large 24" monitor that sits on this desk, and I think it really kills the imaging! Grr!