Dedicated Lines

Being in the same conduit doesn't affect their dedication. They are dedicated if they have their own breaker back at the box.

However, there is another consideration. When you run cables in close proximity to one another for more than a few feet, such as when they are bundled together or in a conduit, then the electrical code(where I live)requires that their capacity be downgraded. So there shouldn't be too many things drawing power from it. How much depends on the size of the cable, the power draw of what is plugged into the outlet, and for what length the lines are together.

I would have preferred plastic conduit rather than metal. Howwever, it is possible that your electrician is using the metal conduit as a ground.

Same conduit is alright.
It would be ideal if the circuits pairs were each twisted (spiraled hot + neutral) for mimimized noise induction between them. However it's done, so don't worry about that. If ground conductors are separate, then they should each be spiraled in the opposite direction around the circuit pairs.

Metal conduit is fine; it is good for RFI shielding.

The 'best' conductor is a controversial question: many varying opinions there. #10 Awg. solid THHN is good. A number of upgrade wire types are also available but some are quite expensive; I can't say if that is worthwhile or not.

Your house ground is the same for everything. Multiple grounds locations can cause major problems with loops, and especially regarding lightning issues.

The audio loads are better off on the opposite phase from your motors if possible. But if they're 240V you have no choice.

Bflowers,

True dedicated circuits do not share the same cable or raceway.

RFI/EMI can transfer from conductor to conductor when sharing the same cable or raceway, (conduit). Also induced voltage from one circuit will transfer from one to the other. Small but still happens.....

If you are using decent shielded power cords on the digital equipment I wouldn't worry about it.

By the way if you want to check the capacitive induced voltage just turn on the power amp/s that is connected to one of the three dedicated circuits. Unplug the equipment from the other two dedicated circuits. Turn off the breakers at the panel that feed the two dedicated circuits.

With a multimeter set the meter to AC voltage. Check to make sure the two dedicated circuits are dead at the receptacles.

Next set the meter to the lowest AC voltage scale on the meter. Test for AC voltage again at each receptacle, hot to neutral. The voltage reading is caused by the induced voltage from the live dedicated circuit feeding the power amp.

RFI/EMI would be the biggest concern though.... jmho.