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!