Margin on speaker sales by high end dealer

You can't look at gross margin in a vacuum.  You need to understand the dealer's monthly overhead cost/cost of operations.  That's why it's so important to push volume through.  Only through volume can you even start to cover the fixed monthly overhead.  If you don't sell enough widgets you could easily post monthly losses on your P&L even if you show a 40% gross margin on a single product sale.  This is really a ridiculous analysis the OP is trying to apply because the equation is far too dynamic for a linear thinker.

The reality is that the vast majority of audio dealers are not getting rich.  The only way to make real money in this business is to scale up large and push a ton of volume through every month.  Music Direct and Upscale Audio do this and probably make very hefty profits below the line.  The rest are hustling for every sale and I therefore prefer to work with the little guy whenever possible.