I went from Class D to Luxman A/AB - And most of what you think is wrong

@atmasphere  Ralph, perhaps I can help a little with SMT question (although you may already know all this) .  Suggestion to use wave soldering for your production is nonsense.  It was replaced by reflow soldering more than decade ago.  The only all SMD done with wave soldering today are low density high production quantity boards  (wave soldering is a little faster than reflow).  Even mixed boards are today soldered with reflow ovens + selective soldering (mini solder fountain).  Limitation of wave soldering is at about 20 mil pitch, but board has to be designed for that (orientation of components) and everything else has to be perfect.  It is perhaps good for 25mil pitch only (compromised adhesion of thin solder dam between pins causes shorts).  Also, board has to be designed for wave soldering in mind since recommended component land areas are different - wider (take more space).  I would design everything for reflow.  Hand soldering prototype with 50mil pitch components is easy.  I can do 25mil pitch large chips with 3D magnifier (Mantis) and micro soldering iron, but it is time consuming.  I've seen technicians who can solder 20mils.  For discrete components 0402 is the limit (already hard to rework).  0603 is practical and easy.  Best bet for small operation soldering would be manual stencil and small 4 zone reflow oven (bigger number of zones is mostly for production speed - faster conveyer belt).  Vapor Phase (drawer style) soldering might be also a good option (more accurate).  Better yet leave it to good Assembly House.  They make prototype quantities and small batches.  They often can buy parts at lower cost.  I went thru about 10 assembly houses before I found one that is wonderful.  Location doesn't really matter since you send them zip file and they ship back boards (leave everything to them!).   Novatronix in Chicago area is the best I know.  Sure, it will cost you more in prototype quantity, not to mention set-up charges, but debugging and testing poorly made board can cost you a lot of time (and frustration, and wrong decisions).  I went thru all this.
For your size of operation Altium software is most likely optimal.

Sorry, for all these details, but it goes toward possibility of making own design class D SMT boards vs using standard off the shelf modules.  The answer is - yes it can be done, many ways.

Except for maybe a prototype, good luck hand soldering for retail production a Class-D that’s all SMD components like this cheap $34 Class-D stereo.
http://store3.sure-electronics.com/media/catalog/product/cache/1/image/600x600/9df78eab33525d08d6e5f...

@georgehifi  
Who said production boards will be soldered by hand?  Many small companies, including one I worked for, make small quantity of very sophisticated high density boards using Assembly Houses.  We used to make them with semi-automatic stencil printer, manual pick and place and 4 zone Heller reflow oven, but using Assembly house  ended up being much cheaper and better, quality wise.  Nobody sane would hand solder production quantities - too much time consuming equals too expensive.  We made batch of about 5 boards for prototyping and then about 100-200 boards in production quantity.  Using good Assembly House opens whole new world for designer (removes constrains).  Now he can design for higher density or even for BGA chips.  

Who said production boards will be soldered by hand?I didn't

I didn't, I inferred if you design a GaN board from scratch, you'd do the whole thing SMD because the GaN semiconductors are all SMD, therefore my statement was.
" They're not stupid and know it's impossible to create a "retail product" complete Class-D board, using all smd components, and making it by hand soldering"

@kijanki Thanks for your elucidation of some of what's involved with surface mount. I think a lot of people think that since we make tube gear by hand that somehow that means we don't have an education or something- or don't keep up with the times. We're using 603 components right now- as you point out, easy to do by hand. And probably too for production- depending entirely on volume of sales! On this basis, this statement:

it's impossible to create a "retail product" complete Class-D board, using all smd components, making it by hand soldering.
You say it can be done, but that would only be a 1 off prototype and not the production version.

-is simply false. Now at some point we may go to 402s just to reduce inductances and resulting ringing and radiation. But for now the 603s have worked out alright. If 'sales' translates to 100s of shipments, then its likely we will farm out the work.

it's impossible to create a "retail product" complete Class-D board, using all smd components, and making it by hand soldering

There appears to be a sleight of hand going on here, compare the above quote above to this one that appeared earlier:

To do that you need to buy either ready made boards then do simple mod and call them your own, if not and you want to do your own GaN Technology boards, you need the knowledge to design it from scratch, and you need some serious automated wave soldering machines to do all those smd parts that are involved, you can’t do it by hand. 

When comparing these two, we see that George had to back off from the idea that 'to do all those smd parts that are involved, you can’t do it by hand'; that's morphed into you just can't create a 'retail product' by hand soldering. Both statements are false. The soldering industry has all sorts of products designed for hand soldering work- and one of my employees worked doing production smd work all by hand.

Except for maybe a prototype, good luck hand soldering for retail production a Class-D that’s all SMD components like this cheap $34 Class-D stereo.

We're not planning to build a $34.00 amplifier and to be clear a $34.00 amp isn't going to have GaN FET output devices- such an amp would be all entirely on one chip. Its realistic to discount that comment as irrelevant.