sounstage too big bad thing

Two things I would check; make sure the speakers are firing at the same point by using a digital level on the sides and back of the enclosures and on top of a board spenning the tops of the boxes to check that their height is exact. Next I would check the isolation of the Quicksilver amps ( they may need better isolation to extract as much clarity as possible) then I'd check the pre.
It is very possible the new cable has exposed something in your system and I would pursue this first before changing the cable.

Almost forgot, the cable may be showing that you need to reduce isolation or change the material.

I agree with Sounds_real_audio and Sns. Distance between speakers and toe-in worked for me. I had a similar issue after upgrading my preamp. In a small room, my chair was against the wall (couldn't be moved further away). Moving the speakers farther from the chair (closer to the front wall) would reduce the wonderful SS depth I had and just couldn't part with.

I experimented by moving the speakers further apart until the SS width cleared up the "congestion" that the enlarged SS created. It still lacked focus. Changing the toe-in gave me the focus. Speaker separation and toe-in interact with my room, so I had to go back and forth several times.

Once compensated for, the increased SS was much better than what I had before. More detail and life-size images.

Relax, have a homebrew and listen to some Marshall Tucker Band...

If the instruments sound like they are over your head perhaps your speakers are tilted back. Do your speakers have adjustable spikes? What are your speakers by the way? Try a higher chair. All of the above. ...

You're getting good advice.

Playing with speaker orientation/location to lock in the new soundstage the way you want is definitely the first thing to experiment with before changing anything else.