Question For My Electrical Expert Friends

I want to move my amp, which is on a dedicated line/circuit. I only need to move the amp eight feet, but I don't want to have to use an eight-foot power cord. Will I negate the effectiveness of the dedicated line (which is one run of Romex from the receptacle to the breakerbox) by coming off of the dedicated line/receptacle with an additional eight-feet of Romex to a newly installed receptacle located eight-feet away from the existing dedicated line/receptacle?

Thanks guys...(and gals!).

As long as you are not using the internal straps on the receptical in the current recepticle to add on the romex.
You need a good solid connectiond of the added portion to the already installed portion.
As long as the connection is solid in there and not some flimsy bit, it should be good.
So making the splice the important bit, and not the connection to the original duplex outlet the priority. Inside that first outlet.

I would make a true equal splice in there, with only a pigtail off for that original outlet. So the current can really flow to the new added wire.
Thanks _E...

I plan to remove the original outlet and make the "splice" Romex to Romex with some wire nuts. I imagine this should not negate the intended purpose of a true dedicated line.
Ensure you ground properly with the pigtail.

Are you using audio grade receptacles or upgraded receptacles that are more sturdier?
Yeah. With the splice being done with wire nuts directly from one Romex to the other, it should be all good.
Make certain the nuts are TIGHT!
And, remember copper will soften over time, so go back a few weeks later and retighten those connections.
I'm not sure there is much of a difference electrically between running a splice with wire nuts and plugging in an additional 8 ft of extension cord, ASSUMING the extension cord is the same or higher gauge than the Romex. With the extension cord you have a choice of using much better multi-stranded wire than the solid wire in romex. Face it, Romex is not high end wiring. Also, if you are using hospital grade plugs and receptacles (or even better audio grade components) I would expect the extension to be better. The extension may not be cosmetically pleasing, which is another issue.

Plus, if the extension is plugged directly into the power amp with an IEC plug, you save the additional interconnect of the splice and the interface contact with the second receptacle.
Don't forget the effect of extra length. Are you doubling back towards the breaker box or extending another 8 ft away from it? If you're going back, then it might be worthwhile to install a new run of Cardas in wall 10ga wire. Another consideration is the benefit of having multiple dedicated circuits and outlets. When I moved my sub to a second circuit, I was surprised at how noticeable and beneficial it was.
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Pigtail the original outlet, solid splice connection from original Romex to added Romex.
A longer (good) power cord is better than moving receptacle 8 feet. If you need a shorter power cord visible, then extending the Romex is okay but not ideal.
An not plug your amp into a small power conditioner with a longer cord that will reach the outlet?Perhaps a Furman?
You need to re-think your power distribution and component layout scheme, making compromises that are acceptable to you (revising amp location may require longer speaker cables; or running a new dedicated circuit and purchasing a second power conditioner; or extending the power cord).  Technically speaking, any choice that maintains integrity of your power distribution system is correct.