What wire to use instead of Romex

No help here, sorry. I was under the impression that solid core is code, though I am sure someone else can comment. I just ran Romex for my dual lines, but it is only about 15 feet.

Depends on the local code requirements that your HOA is following. In some states, though not common, hollow (metal/Alum) conduit is required to be bent and set, then solid wire fished through. MC flex cables may only be used for certain lengths of runs. It all depends... If you don't know your local code requirements, as said before, consult your electrician first before picking products. A licensed electrician will know the code.

Use an electrician for installation. But specify the wire. They will think you are crazy, every time I have done it they have. They will refuse to believe that different wire sounds different. I just asked them to humor me. Definitely 10 gauge. I think there is specialty wire. I'm sure someone here will specify it.  I used 10 gauge Rolex. Excellent improvement in my system. 

Because of HOA rules/regs, I cannot use Romex. Wires in the garage must be inside conduit.

That also may be the AHJ (Authority having Jurisdiction) electrical code in your area as well. In Chicago IL only EMT conduit is allowed in residential housing. MC or AC/BX, nor flexible metal conduit is allowed. Going from memory in NY City, NY Romex is not allowed.

You need to contact the Electrical Contractor you will be using. He will know what you can use. Also have a copy of the HOA requirement for him to read.

As for using EMT conduit I would suggest you ask the Electrician to twist the Hot and Neutral conductors together before pulling them in the conduit. Pull the EGC, (Equipment Grounding Conductor) along side the twisted pair when installing the branch circuit wiring in the EMT conduit. The EGC could be #12awg green insulated solid copper wire if you use #10awg copper wire.(FWIW, the electrician may tell you you don’t need an EGC insulated conductor in the conduit. Per NEC the EMT conduit is an approved EGC. It’s your call... I would have him install the EGC insulated conductor anyway.  

Solid core wire only for the Hot and neutral conductors. Tell the electrician you want solid wire not stranded. He is going to resist the suggestion. Hold firm.

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The run from the main panel in the garage to my living room above is relatively short - maybe 25 or 30 feet.

Did you guesstimate Up, over, across, and down?  

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Some reading material for you:

An Overview of Audio System Grounding & Interfacing

 Read page 16, and pages 31 thru 36.

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Integrating Electronic Equipment and Power

Read pages 11, 12, &13. 

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@jea48 @ghdprentice @nwres @zlone @ditusa 

The distance measurement is a down-over-across-farther down rough measurement.

Flexible conduit is allowed by code. My town's fussy code inspector saw what I was using for me EV charger outlet run and was fine with it. Romex is perfectly acceptable too as far as code is concerned, but not a good idea to put inside conduit. As I said before, the HOA wants any wires in the garage inside conduit, presumably for a uniform appearance as the garage is a shared area with four bays, one for each condo in the building (there are 86 buildings).

I fully expect to get a funny look from any electrician when I specify, "Metal Clad (galvanized steel, not aluminium) 10 AWG Solid Core Copper w/Insulated Stranded Ground. Twist the hot and neutral together before pulling the wires and run the ground along side."  I'll just shrug my shoulders and smile when he shakes his head and/or rolls his eyes.

Thank you all for the input. It's very appreciated!