Elvis, though I use NS Garnet almost interchangebly
I'm still a little skeptical, but since you already have 4 concentrators, have you looked into this setup from High Volume Oxygen?
http://www.youtube.com/watch?v=Mq_u7qjOwTM
The demo showed them using a bank of 6, which is awfully spendy on top of the HVO units. But like I said, since you already have 4...