If you had to do in cabinet speakers

Do you mean in-wall ?

KEF have some nice "in wall" speakers.

For the cabinetry, try investigating folded horn designs.

These may allow you a bit more flexibility and could potentially solve some of the problems that downward firing mid and HF units will otherwise cause.

Directionality will be the biggest issue - to that end, the KEF Uni-Q based Ci200Q models (one square mount, one circular mount) would be quite good.

Once you get beyond a coaxial design, you have to consider phase & timing issues that may not easily be changed after the drivers are mounted.

I assume the cabinetry will be custom ddsigned for the application rather than just sticking a couple of 'ceiling' speakers into a flat pack cabinet.

If you're just putting speakers into a normal bit of furniture then it doesn't matter that much what you use: Unless you use really cheap drive units, the cabinet(s) will be the limiting factor in the SQ.

On the other hand to do it properly will require quite a lot of calculation (and take advice from the people who supply DIY kits for speakers).  There are designs for DIY horn speaker enclosures that can be used as the basis for a reasonably competent design that will control the directionality of the sound and give a reasonably even frequency distribution of both the direct and the reverberant sound.

David,

The original post specified downward firing drive units; I'd be concerned with the KEF concentric system that the MF & HF would be unevenly absorbed and reflected by both the void under the cabinet and the material of the floor.

IT may be possible to use a downward firing bass mid unit (with a low crossover frequency) combined with a forward facing tweeter, and to run the bass mid in compression driver mode.  To do this requires that there is only a small clearance between the bottom of the cabinet and the floor and there's a rigid reflective surface below the speaker drive unit.  This results in an effectively annular cavity coupled driver.

If the cabinetry is solid, and large enough, and effectively a wall, you have the potential for very good speakers as rear reflections are eliminated - however from your mention of downward firing that sounds more like an overhead cabinet? To avoid losing the treble that may need a ceiling design for mid and high frequencies at least, with for example a conical reflector, or could you use smallish satellites below the horizontal surface and have bass speakers built into the cabinetry above?

Many thanks to all for the replies. Here is a little more detail to see if it changes anything.....we will have a line of cabinetry over a king size bed . It will be quite a wide run about 10 ft in total. The bottom of the cabinetry will be about 8ft off the floor (thus about 6.5ft off the bed) and the speakers would fire downwards onto the bed. There would be soft material on the wall behind the bed. 

Given this I am inclined to thing that the top option would be the PMC Wafer 2 and 2nd option would be the Kef square Uni Q line

Any additional thoughts? 

It would have been a good idea to explain what you were actually trying to achieve in your first post.

You've also now introduce the fact that this will be a near field listening situation.

You've still not specified how wide the listening zone is (1 person centrally or two people on the bed). 

You've not specified the size of the cabinetry (top to bottom and depth from the wall).

All these affect choices.