Soundhound is right about how a circuit breaker works and affects voltage. You should not change a circuit breaker existing in a panel to a larger size!!! This could allow the wiring to overheat and cause a fire. I don't feel the current size of the circuit is your problem. Your not tripping the existing circuit breaker. I feel your problem is a voltage drop issue. What you are looking for is a dedicated circuit fed with a new 20 amp breaker. It's possible your stereo is on a circuit with something else causing a voltage drop when turning it on. The dedicated circuit should eliminate the dimming problem. The reason I suggest a 20 amp circuit is the wire has a larger size diameter allowing less voltage drop to the outlet. I disagree with the 30 amp circuit. Your equipment's plugs wouldn't fit in a 30 amp circuits plug!

A GFCI is a Ground Fault Circuit Interuppter. This is used where an electrical device is used around water. Not usually needed for HT.

I've been master electrician for 20 years, building hospitals and haven't seen or heard about a hospital grade breaker. Usually, hospital, and commercial, circuit breakers are bolt in style. They have a screw that holds them in the panel. Most residences have plug in circuit breakers and bolt in circuit breakers won't fit.

They do manufacture a "hospital grade" receptacle. I feel this would be over kill for HT.

Cost for this job depends on the difficulty and area of the country.

As you have said a professional is your best bet. I hope I have made things a little clearer for you. Good Luck. Jim