l wanna install a headunit into my Scion Xb 2004 with two 10inch subs. How do l know that it will fit in the dashboard? Do l need to buy an adaptor. Also what do l look for in the specifications to make sure that it will work with the subwoofers.

if you go single din your gonna need dash kit and a harness wiring adapter. double din you wont need it a dash kit but still need a harness. as for a head unit make sure its something of quality anything now days over 150 bucks should do what you want it to do.
dash kit pn#
setra
70-1761 Harness
99-8209 Kit

American International
TWH-950 Harness
TOY-K969 Kit

Scosche
TA02 Harness
SCN2056 Kit

You will need a new face plate, an adapter to shut off amps in speakers, and one for wiring. Who ever sells head units will have a chart to tell which will fit but anything can be made to fit. Cost is around 125.00. It will be like hooking up stereo in older cars which have no amps in speakers.If you hook up withou adapter you will blow unit and speakers in about an hour.t