Well I think they still are!
HT 5.1 needs 5 speakers LF-C-RF then LR-RR and if the fronts do not have realy good bass, add a sub.
I don't remember anything about your speakers.
You could use them as the rear and get new fronts and center speakers and HT reciver.
Or use them as the RF-LF add a center, add L-R rears, sub and HT reciver.
You should try to get speakers that sound similar to your Quart 1s. John