Wiring main panel box for dedicated 20amp line.

I'm getting ready to install a dedicated 20 amp line and came across something I wasn't expecting. I have a single GE main panel box that's about ten years old. When I opened the box I was expecting to see neutral wires at one bus bar and the ground wires attached to the other, with the black wire - of course - attached to the circuit breaker.

Instead, I found the neutral and ground wires for each outgoing wire attached to the same bus bar on adjacent screws. I've since read that this is common practice and apparently up to code on a main panel.

To install a new 20 amp line, I could duplicate this setup with adjacent vacant spots on one of the bus bars and a new breaker, but I'm wondering if using a common bus bar for both the neutral and ground wires is suitable for a hi-fi application? The whole idea is, of course, to have a dedicated, properly grounded circuit for my gear. Also, if it's not ideal, would a small sub-panel be a desirable solution?

I'd be grateful for anyone's expertise. Thanks!