Your One Bullet Point Solution; Electrical Upgrade

Sure, now I need a car upgrade!  ;) 

@douglas_schroeder 
Your dedicated circuits to your audio room could be protected by a individual 20 amp breaker with its own surge suppression built in most manufactures sell them Square D, Siemens, etc. I would also have the electrician test your grounding electrode system and make sure your reading from ground to earth is 25 ohms or less to ensure its integrity is up to the task of dissipating faults even small ones in the system. Also if you keep your sub panel and just change the main have your electrician make sure the downstream sub is properly wired// grounds and neutrals are separated and only bonded together at the source. You would want current flowing on the grounds. 

I’ll add a few opinions, although I’m not a professional electrician or a NEC expert.

First, I’d heed tvad’s suggestion about a circuit to the garage. I put in a 50 amp 240V circuit when I had my house built, yes with the plan to get an EV (which I did). However, having a circuit to the garage will be a benefit to somebody at some point who would want to do a workshop, welding, etc., so it is cheap to put it in now, much more expensive later on. I’d also put in a 20 amp 240V outlet right under the main panel, just for an air compressor or something you might want to run from 240V.

Some have mentioned the grounding rods, and rather than test if the one is at specification, it seems easier to just put another one in, according to code of course.

I see absolutely no reason to remove the 100 amp panel to the HT room, it is better to have it and not need it than need it and not have it. That is the same justification for upgrading to the 200 amp main panel. Also, just because it is a 100 amp subpanel, if the loads on the panel are calculated it can be supplied by a lesser amp (for example 60 amp) breaker.

One other detail I’ve learned from listening on Audiogon, the dedicated 20 amp circuit is a major focus, it seems you might be able to do a couple to the HT room. And to go even with 10 ga wire.

If I was redoing the electrical at my house, I’d have added several conduits in various locations where wire could be pulled easily at some future point.  A roll-you-eyes but I still would LOVE to have it, a 20 amp 240V circuit to the living room or bedroom, where I could power my computer with the more efficient 240V.

You have a computer that uses 240?

You might want to consider a Power Conditioner.  It takes care of surges as well as smoothing out power dips and other power line induced noise.