I think your electrician is giving you the more economic solution with a sub panel vs. a complete replacement.
If you already want to replace the main panel anyway, say to clean up code violations and/or breakers being used for more than 1 run, then sure.
OTOH, if your listening room was 60' away, and you wanted to run 4 or more independent circuits then a sub panel would be a really good idea.
Also, never underestimate what you may discover and have to pay for with a complete replacement. :-)
If you already want to replace the main panel anyway, say to clean up code violations and/or breakers being used for more than 1 run, then sure.
OTOH, if your listening room was 60' away, and you wanted to run 4 or more independent circuits then a sub panel would be a really good idea.
Also, never underestimate what you may discover and have to pay for with a complete replacement. :-)