Dedicated AC line - Contractor wants to use BX instead of romex

WOW I am a recently retired electrician (35 years) and what needs to be said here is we need to be careful of your opinions when you don’t have the knowledge. This could be dangerous to life and property. Sometimes the local codes are contrary to what we want for our high end audio. There are reasons for the local amendments to the NEC and these local amendments must be adhered too. I’m not going to try to educate everyone on this site but some of the answers show a lack of understanding to the trade. This is where the danger is. When we choose to ignore this that is where we get in trouble. 
Always remember the NEC is written to prevent electrical fire which are usually catastrophic. 
I love my audio like we all do but not at the cost of life safety. 
Enjoy safely 

Considering that pretty much every state has as law the National Electrical Code, what place where laws don’t matter do you live? Cities often take these things more seriously because fires don't just take out one house, they can take out a whole bunch.

The problem is a lot of cities and townships in the us don't really take it seriously. In my city the inspectors don't even have to be licensed, they go to courses but end up playing golf as they don't have to sit through the whole course. When I installed a new service in my house about 30 years ago, I had a 40 amp breaker on a 20 amp circuit and they passed it.