I have the 1.7i in my main system but use a sub in my 2.1 bedroom system (mainly used for home theater) with the LRS+.
I would suggest trying a sub which allows you to pick a slope (I use 24 db/octave) and has variable phase (I found 90 degrees works best in my room).
The funny thing is that except for earthquake type effects, I found the bass from the LRS+ (using my old Adcom 545 II) to be more than adequate for watching movies.