dedicated circuit, flex conduit?

It has been recommended to me to use 10 gauge solid core romex for my future dedicated 20 amp circuits, (I plan on using two, one for digital and one for analog). My speaker manufacturer recommended using flex conduit to help RF, etc? My understanding is this cable comes with the wire already in it. 1. Can any of you relate your experience with flex conduit? 2. Do you need to ground the conduit? 3. Also, it has been recommended each circuit should have its own hot and neutral with each sharing a common ground amoungst them. 4. Is there anything else I need to tell my electrician?5. I have only 5 spots left in my panel for new circuits, would I benefit from a sub-panel?Thanks in advance for any input.
Sorry, I entered this question twice. But my computer locked up when I first submited this question so I entered it twice thinking it did not post. Please ignore this post.
1. Wire in metallic conduit is the superior wiring method since the conduit provides shielding. I'd lean towards EMT with compression fittings over Type BX (what you call flex).
Neither one of these is a breeze on a retrofit; actually nothing is a breeze on retrofit. Typically, your into a lot of sheet rock demo and replace. It totally depends on where your panelboard is in relation to where the intended outlets are.

Fishing and terminating #10 solid is *not* easy. Go buy a cheap receptacle and 18" of THWN and try it yourself. This
is very large and stiff stuff. But that is what I'd spec.

BX is available pre-loaded. This is typically used in commercial app's for fixture and switch wiring.

2. Of course. You'd embarress yourself by posing this ? to an electrican...

3. ? The preferred option here is the widely misunderstood isolated grounding method. An individual green ground wire for *each receptacle back to the panelboard. IG receptacles not required for use with plastic outlet boxes; they would be with metal boxes.
The ideal is one receptacle per branch circuit breaker. If not, isolated grounding methods should be employed.

4. Yes, let me see your IBEW Journeyman cert. Yes, you *will torque all terminations to mfgr's specs. No handymen need apply...

5. Not really. Depends on the age of your existing system. I'd be inclined to drop in a brand-new panelboard while I'm at it,(Square D brand), and for myself, I'd go for bolt-on breakers vs. stab-in's. Everything Pro-Gold'ed and torqued, of course. Have the terminations at the service panel - including the ground rod connection - cleaned and torqued. You'll have to have the utility do a disconnect to do the line connections at the service...