Depending on how much you want to spend you might want to see if there are any PSB resellers in your zipcode. About a year ago I spent a significant amount of time at AVS and Audioholics trying to figure out what I wanted. I drove around and listened to various sound systems. I took a bit of a gamble (or so I thought) on the T55s from
http://saturdayaudio.com/picturepages/image_specials_07-29-2009.htm#T55.
I have never looked back - I absolutely love them. The sound reproduction they are capable is fantastic. They are also stronger on the bass than most of the other speakers I listened to without being boomy. Compared to the VR3s and M50s I had they don't lose their definition/clarity at higher volumes either. The PSB speakers are very easy to drive (6ohm vs 8ohm). Looking at the Monitor 70s the PSBs have a much wider frequency range and sensitivity - but they are more expensive as well
I bought the Monitor 50s (It may have been their R50s I cant remember for sure) but ended up liking the Boston Acoustic VR3s better so I sold them. They lacked too much power especially in the bass for me. The VR3s are still in our family room but the projector in the basement was just begging for more - which was why I got the T55s
That said pretty much anything will be better than the Logitec's (Nothing against Logitec - I still fondly remember my 5.1 computer system)