I registered just to help you out with this. I havn't even gotten my Z yet but I've been researching for a sound system for about a few weeks now. The first thing we gotta know is how much money you willing to drop for a system.
I'm looking to spend around 3k, this includes a doubled in head unit, component door speakers and 2 12's in a custom enclosure powered by an amp for the door speakers and an amp for the subs.
I've been to all the major department stores and well they got nothing you can use. It's all low end stuff or brand names that are just over rated.
I've been jumping around on products I want but so far these are what to consider for now;
Head Units to consider Kenwood Excelone 9140 navi or last years 814 non navi. No other head unit offers 5v preouts, 13 band equalizers and an advanced graphic user face.
Door Speakers to consider Boston Accoustics. Everyone talks about them but it takes money to get their good stuff, MB Quartz and infiniti kapas are good but only if you like lots of treble. Right now kickers are selling their Rs series for a real good deal and they are the bang for the buck right now.
Sub woofers I'm considering are JL's only, The w7's are very loud but the w6's have better control and overall sound quality.
My best source is a friend of mine who owns a Audio shop in LA. He caries every brand you can think of and gets the newest electronics first since he's in cali.
Here's his website
http://www.armexcaraudio.com.
I hope that all helped