DO NOT lay the wire on top of the ceiling-especially a drop tile one.
Yes, please leave that area clear for the HVAC, CCTV and Telco guys!
But seriously, I can't remember the last time I've installed speakers without integral steel back-cans!
A few times I've had to forcibly remove tops of old plastered-in cans to fit EVID's before.
All we do now on pre-wire for new-builds is place the steel rough-in rings for the finish contractors to go off of.
I've found that "canned" speakers sound better because the manufacturers are working with a known size and can port and tune accordingly. Open-backed residential home stereo speakers have always mystified me in that how can they spec the LF frequency response when they have no idea what size space or insulation (if any) is going to be behind the speaker?