[nikongod]

no.
 
If the amp[ happens to have balanced outputs, bonus round. 
 
If the amp is single ended the grounds connect somewhere in the amp. 
 
You wire the headphones with separated grounds because there is no real way to know. Well there is, but murphy's law dictates that if you build something that is easy to use incorrectly (a speaker amp to TRS female adapter) with possibly destructive results it will happen. So dont. 
 
The only downside to using a 4-pin plug is that you have a 4-pin plug. After the fact that it is not the most common standard it is alllllll better than TRS.

 

[BMBROWN911]

Why would speakers each have a separate ground then if they are common inside the amp?

 

[nikongod]

I have misused the term ground. I will beat myself mercilessly with the 4-pinXLR on the end of my HD800 cable. Or not. 
 
Speakers use separate wires for all 4 connections because speakers have no ground connection. Speakers and headphones have "in phase" and "out of phase" connections. NOT ground. I misspoke. I'm sorry. It is amplifiers and other electronic devices that have grounds, and it is not until you hook the speaker up to one that it has ground. 
 
Not all amps connect the speakers to ground. Balanced amps for example. 
The impedance in a long single shared ground cable would possibly lead to funky cross-talk issues with speakers. I'm not so convinced with headphones, but since no good headphones have a shared ground wire I have to assume there is a reason.  
And perhaps best of all - with the common arrangement of the speakers off to the sides and the amp in the middle there is no real reason to do it.