I just received the MBQuart rear shelf speaker adapters I ordered through the local MBQuart dealer, and I was surprised to find out that the adapters are designed to hold 6 1/2" speakers. 5 1/4" speakers could possibly be mounted in them by suspending them over the gaping hole with brackets, but that doesn't make too much sense!<p>The MBQuart Web page claims the adapters are made for 5 1/4" speakers and that information was confirmed independently by Brian Sherman of MBQuart via e-mail. Based on that information, I had ordered a set of 5 1/4" speakers. Now I suppose I've have to send them back and get a set of 6 1/2"s instead (which I prefer, so it's not a great loss).<p>The MBQuart Audi front speaker adapters are good for 5 1/4" speakers.<p>Before anyone asks, the front adapters are $36/pr and the rear adapters are $44/pr through your local MBQuart dealer.<br>