integrated amp - jumper between preamp and amp

If you have a pair of RCA interconnects, plug them in to see if you notice anything. If you like what you hear, then you can consider buying a shorter "jumper" set.

The good news is that McIntosh had the wisdom to do this with jumpers instead of a mechanical switch with internal circuits.

Most audio gear is now and has almost always been designed by engineers who are skeptical of magical thinking. The big change came in 1980, when Richard Marsh published his treatise on capacitors in Audio Magazine. Soon, the race to impress with boutique caps was on, led by Levinson and Conrad Johnson.  The arrival of “greed is good”, and the onset of the meteoric rise in income inequality all corresponded.  The post-war period when the middle class was ascendant gave us Dynaco at one end and Marantz at roughly a 1:4 ratio of cost between a Mark lll and model Nine as an example. Those engineers were grounded in elecrtonic knowhow, and were careful to avoid the wasteful use of unnecessarily expensive parts. Silver plated teflon insulated wire is just another example of this. 

@easystreamer and @dynacohum your comments are very helpful, as in fact are all comments in this thread. I miss the Dynaco components I assembled as a teen. Despite my respect for McIntosh engineers, may try a pair of RCA cables before venturing to explore the silver rod idea that would, at least, match my aged hair.

Boutique Parts' are primarily associated with their cost, as a result of low-volume production, hence, a notable markup is charged as the sale price.

Other components, which are the common selection, will be from a much increased production volume; hence, the cost per unit is much lower. 

My experience is that a change to a component's value will create a notable change in the end sound being assessed. Whereas swapping out like-for-like component values has proved to me to offer very little in end sound change as a result.    

Anything you think you hear would be a placebo effect.  Think of it this way, those jumpers are quite a large gauge of metal, connecting the preamp and the amp boards inside.  They are much larger than the traces on the circuit boards they are connecting.  Essentially, the 2 small traces on those boards were moved outside the chassis and severed.  Then those large u-shaped jumpers were installed to connect them.  Those jumpers are also much, much larger than a RCA jumper that you could install there.  The wire gauge inside most all RCA's is tiny.  Possibly smaller than the traces on the boards.