Most Beneficial Cable Upgrade

There is a lot of subjectivity here. But one cable that is extremely important and must be taken care of is the interconnect from source to preamp. It is true for every system.

However in my system it is the power cord to the source that does the most.

In my experience the most important have been the interconnect from the source, speaker cable, and the power cord to the source.

In my system, it seems as though the preamp to amp interconnect makes a big difference.

at the very least step up the quality on every cable first.

I would recommend something like VH DIY PC and Morrow or Signal or Blue Jean ICs and speaker wire.

In other words do not get ICs and speaker wire but ignore the PCs, there is too much to be gained from good PCs.

There is a big step up with the initial move up from stock cables in every location.

fwiw in case you have not considered this...

Following are some factors which will affect the answer to your question:

1)Sensitivity of the system to interconnect cable differences will be increased if:

(a)The output impedance of the component driving the cable is high.
(b)The cable is unbalanced (rca) as opposed to balanced (xlr).
(c)Ground loop effects involving a particular pair of components are present, as indicated by low level hum, buzz, or noise that goes away if a cheater plug is placed on the power plug of one of the components.
(d)The cable is carrying a phono-level signal.
(e)The cable length is long.
(f)The existing cable has high capacitance.

2)Sensitivity of the system to speaker cable differences will be increased if:

(a)The speakers have low nominal impedance.
(b)Speaker impedance is low in the bass region.
(c)Speaker impedance is low in the upper treble region.
(d)Speaker impedance fluctuates widely as a function of frequency.
(e)The speaker requires tight woofer control and high damping factor from the amplifier.
(f)Cable length is long.
(g)The existing cable is marginal in gauge.
(h)The existing cable has high inductance and speaker impedance is low at upper treble frequencies.

3)Re power cords:

(a)Power amplifiers and components containing significant digital circuitry tend to generate high frequency noise, which can couple from their power cords into other system components, with unpredictable effects. Therefore using shielded power cords on power amplifiers and on components that contain significant digital circuitry can be important.
(b)Some power amplifiers are particularly sensitive to line voltage differences, and therefore to voltage drops that may occur if large amounts of current are flowing through their power cord. If there is reason to believe that the amplifier's power cord is marginal in gauge, or if the amplifier is specified as requiring large amounts of ac power, its cord should be particularly focused on.
(c)Keep in mind that rfi/emi effects can be affected by physical placement of the components, and the physical routing of their power cords and cables.

The bottom line: As Stan indicated in his first post above, there is no universal answer. But consideration of these factors can reduce the randomness of the process.

Keep in mind, also, that more expensive does not necessarily equal better. What can be expected to matter most is how the cable interacts with what it is connecting.

Regards,
-- Al