I am listening to music using a pair of ML motion 12s and my old JBL L88s. I added the JBLs to provide some lower end bass the ML don't have and the combination has been very pleasing. However I am about to hand down the JBLs to my son and I am beginning to consider other options. Would like to hear some thoughts on adding a sub vs adding some less expensive speakers that might fil the base needed. Would like to keep the cost under $600. This is for a small 150 sq ft listening room and I listen mostly to R&R, jazz on vinyl so I am not looking for booming bass. Running speakers from a Cambridge 650a.