Dedicated 20 amp circuit. 10/2 or 10/3?

10/2 and run more than one dedicated line while you are at it.

I have a pair of class A mono blocks, I ran one 12/2 conductor twenty amp circuit to a Cardas 4181 receptacle. From the wall the power cord goes to the power conditioner, then all my gear plugs into the PC. Running full load with some volume, I am pulling 9 amps of current . Not sure what your gear is? #12  is adequate for most systems. But run cable for where you will end up.

Keeping all the audio on one leg helps reduce ground loops. Your system is probably not going to draw enough current to need both legs.

Circuit breakers at the Bus? If you are running a dedicated breaker for each piece of equipment (you are going to need some 2 and 5 amp breakers, and with no AC motor loads I would ask why have a separate circuit for everything?... I would first consider a sub panel to save on all those copper runs (and to prevent leeches, or "other" circuits invading), then yes alternate between the bus (legs), or left side right side in the panel, and try to keep the loads balanced, and the circuit breakers and wires correctly sized for the designed load ("over sized" circuit breakers and wire is not a CURE for anything). Any 220V breaker will already be feeding from both bus bars. Chances are good that your main panel is presenting an unbalanced load now. If a sub panel is separate (downstream) from the main service, through a  fused disconnect and a sub panel main breaker, I would consider Isolated Ground Outlets, and possibly (if the current NEC allows) a separate grounding systems for that sub panel, or at least those outlets.  A more extreme$$$$$ (but effective) measure would be a complete new service, much like Fremmer did at his house (see his videos). But please consult a Master Electrician, I have not professionally practiced since 1994, and am not familiar with current (lol) code.. The National Fire Protection Assoc. publishes the updated National Electrical Code, and licenses professionals in an attempt to keep us folks from burning, or exploding, things and those we love and cherish.

I made all the stupid mistakes with power that are possible, including not checking the electricians work when he set up a reversed neutral one of the times they wired my room. 

I have a large house with sub power panels, I didn't take my home run lines to the main panel but to a sub panel. Stupid I know. But then again if I did go to the main power connection to the house that is still a sub branch of the power on my street and in my part of the neighborhood. So I bought 2x power reconditions PS Audio P20s and I already had about 5 different kinds of old power conditioners from studios. 

I have lots of powered speakers so I need different legs simply for current. If you don't have to use different legs you are better off because there will always be a different voltage between neutral and ground on separate legs, the voltage difference between neutral and ground is buzz. Yes get the biggest gage cable you can, it doesn't hurt especially that in the future there will be a lot more current usage for powered speakers.

Power is odd it's very simple and at the same time can be a mystery and suck lots of money towards ends that don't make audible differences in the sound of your equipment.