I'd assume the LFR's in a 5.1 will give you a similar sound field as you would get with a 7.1 setup using front presence speakers.
I'd say the LFR's are more enveloping than those without them realize... it's a hard thing to convey without the experience.
I started with M80s and still have them for heights(I love seeing them up front) and have them set up on my subs. But that is for movies mostly.
The LFRs are mainly for music and BD concerts but sounds better than any theatre for movies, that's for sure.
If you do get the LFRs, make sure that you get the DSP 3board for your VP180..enjoy whatever you decide!
Yeah. M80's as heights... and he gives me a hard time over my subs.. *rolls eyes*
Here is a picture of my setup
VP-180, LFR's, as well as Dual EP-600's.
The amps are Krell kav-250a/kav-250a3 and a Krell FPB 300cx the 300cx is power the front drivers on the LFR's an the 250a is powering the rear's the 250a/3 is powering the center and the surrounds.
Depending on the source material, the LFR's can be Amazing. I would say the determining factor should be what your going to use the system for. Do you listen to stereo music at all? This is one of the primary areas where the LFR's shine. As well as a well mastered Blu ray movie or concert.
If you're going to use the system primarily for TV, and an occasional movie. Then i would tell you to save your money and pass on the LFR's.. However, if you already listen to a decent amount of 2 channel, or blu ray music then i would say it would be worth the extra cash...