Well it all depends on your budget, and yes if you do want those head rest monitors, then you will have to buy a head unit that will support it, and Really i been thru alot of car audio equipment and trust me you dont want a no name brand, its better to go with a brand named head unit.
When bying one look for :
Whats ur budget like?
What functions you would like to have, (ex. My friend has one that also takes in a memory card or usb stick, and he just downloads movies onto the stick and plays it via usb stick, which i really think is cool!!)
Also honestly i say u save a bit of money and get a really good deck, because you can use it on the next car you buy as well,
My recomendation is to buy one with dvd and navigation
and sat radio!!!
and for the e36 its better to buy a 1 din in-dash Head unit, dont buy the cheap In-Dash because they will break on you, (ask em how i know
) , buy a good one like the alpine IVA series