I too took advantage of the special intro price on the LFRs and am very happy. However if you mainly use your system for multi-channel (music or HT) the M100s may give you most of the benefit at a much lower price.

It may be obvious but to add the LFRs to your system you would also need to add an amp. So unless you also want to move to 7 channels... Oh wait it looks like you already have 4 QS8s? And I guess you could use some of the available amp channels in the MRX?