if you have an Alpine head, go with an Alpine processor. you get AiNet control and optical input (so the volume on the alpine head unit controls the volume on the processor). any other brand will require you have a separate volume control for that processor when using an optical input.
you have several choices in the PXA line - each with a different controller.
but the only processor made to keep up with the quality of the F#1 line (the CDA-7990 is F#1) is the F#1 PXA-H900 processor.
The H700 and H701 are noisy.