A/C Mains. Solid or Twisted

Much of the dialog and opinions circulate to run an a/c main of at least 10/2. My family of electrical contractors indicate that it’s almost impossible to “fold” solid 10/2 wire into the outlet box. They suggest the stranded 10 wire which is as they have commented the largest that is allowed by code if stranded. They could be wrong.  Is there away around the stranded if necessary OR is there a difference in sound between solid and stranded In sound?
In speaker wires” Morrow “ seems to believe there is as , in the past, George Tice was a “solid believer”. Tice cables, amazing bass IMHO! 
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I also wanted to post this response from an agon member.
Thanks Posted by rcrump (M) on February 5, 2004 at 07:15:55 
In Reply to: Re: Why solid over stranded??? posted by Jwm on February 3, 2004 at 06:20:47:"
Thanks DeKay,
Solid 10/2 it is. Pass the 60hz, not the RF.  Will have the camera ready when the electrician tries to fold it into the outlet box. Probably best to do with open wall access and double metal duplex box with a single duplex adapter. Other comments welcome.