Outlet is "Open Ground" - Is There Still a Safe Way to Connect to My Audio Gear?

@erik_squires

You should get the grounding issue fixed, but the only "fix" for this I know of is to use a GFCI outlet and label it with the sticky labels that say "No Equipment Ground." 

This is what NEC code calls for. Had to scroll too far down for to finally reach the correct answer. You can also replace the first receptacle on the circuit with the GFCI and attach the downstream receptacles to "load" and label them per above. This will ensure each receptacle on the circuit is protected by the single GFCI. Or place the GFCI solely on the receptacle in question. 

@jea48 

The replacement GFCI breaker is a good alternative, if somebody manufacturers a retrofit for what is likely a 60 year old breaker box. Ideally, OP would hire an electrician to install a dedicated 20 amp circuit and verify that the sub and main panels are properly grounded too. 

I figured a replacement GFCI outlet was the simple "fix" he requested, however, his wiring does add another layer of complexity. The grounding issue could easy snowball into a large, expensive project.

Agreed, the best fix is to hire an electrician. 

**406.4(D)(2) Non‑Grounding‑Type Receptacles.**

Where attachment to an equipment grounding conductor does not exist in the receptacle enclosure, the installation shall comply with (D)(2)(a), (b), or (c):

(b) A non‑grounding‑type receptacle(s) shall be permitted to be replaced with a GFCI‑type receptacle(s). These receptacles or their cover plates shall be marked “No Equipment Ground.” An equipment grounding conductor must not be connected from the GFCI‑type receptacle to any outlet supplied downstream.

(c) You may also install a grounding-type (3‑prong) receptacle without a ground, if it is protected by a GFCI (breaker or receptacle). In that case, the receptacle or cover plates must be labeled “GFCI Protected” and **“No Equipment Ground.”