Stranded vs Solid Copper

I did the same thing a few years ago. Use 12awg solid copper Romex and connect to an unused circuit with 20 amp breaker. By the best breaker you can. Try to use the leg with the fewest appliances and large power draws.

Thanks for your response.
Luckily the circuit is 5 outlets with one overhead light. I never turn on the overhead light and typically use one lamp. It would be nice to have a dedicated circuit, but I didn’t build the house.
What I’m asking if 12 gauge stranded wire has inferior sonic characteristics? It would make a more flexible cord. I’ll look into a better breaker.

 IMO it depends on your system..The more resolving the system the more likely to hear a sonic difference IMO favoring 9nines solid or better...

I assume the other 5 outlets and light are wired with Romex 12/2  if it's a 20amp circuit back to the breaker box. I guess using 4 or 5 feet of stranded at the end of this run might make a sonic difference but I really don't see how. You can use stranded and it is more flexible though it should be terminated at the outlets slightly different than solid to keep the strands tight. 

Not getting the point of a home made box, hospital grade receptacles will fit in standard boxes. Not  sure home made would meet code might want to check on that, if there was an accident insurance companies can get a little testy  on such things.