(meaning headunit and amplifers) look at the SNR ratio and THD numbers. You want the SNR as high as possible (>100dB at least) and THD as low as possible. IMO, these are two of the biggest specs that relate to sound clarity/quality. Also, you don't "need" monster cable brand cables. Look on Ebay for some Phoenix Gold or MTX cables. I purchased some very nice MTX gold plated cables for like $20/pr.
My screen name explaination: http://www.twinturbo.net/net/viewmsg.aspx?forum=general&msg_id=1186059