Hard Wireing?

Agreed with the prior post about
(A) not doing it yourself.
(B) do not simply hardwire a thicker gauge cable; use a quality female plug to facilitate the attachment of a quality external power cable.
(C) replace the crap wall plugs with (at a minimum) hospital grade wall receptacles.
(D) a dedicated power line to the breaker box is the logical extension of this (eventually).

Without prejudice to (a) and (b) above, Not sure whether the cost / reward on your receiver will pan out for you. I would have the qualified technician assess it for before you jump in.

Good luck

Agree with Csontos

(1) If you capriciously hardwire in a new power cable, you may trigger a safety issue. If it causes a fire or damage, you probably violated / nullified your insurance coverage

(2) Without prejudice to the above , IMO the potential performance uptick of doing it in a receiver without the higher end power supply, likely just isn't there.

(3) Add to this the added cost of having an IEC female plug dremmeled and soldered in professionally ( if it can even be physically done with the crowded layout in a dated receiver) and then purchasing a quality external power chord , again likely isn't worth it.

If it's not working for you, trade up to new gear instead .