Vandersteen 2C contour controls +-

Update:

After letting the cables sit without change for over a week the bass came back 80% which is fine - I was a little bass heavy before. More importantly, it really only shows up after letting the entire system warm up for a few hours. Previously I'd get up to full range in an hour or so.

I've now put a bit shy of about 200 hours on the cables.

I think this lends to the dielectric properties theory. The new cables are just more difficult to charge than the other ones. The end result is a better sound in my system.

That is great to hear. I bet when you hit 400 hours, things will be even better.
Bob

Alternatively, perhaps the mid and treble controls are turned up too high in relation to the bass at any given sound level.  Their relative setting to the bass may have changed from the old to the new wires.

@jetter 

I've set the contour controls on the speakers at 0 during this time.

I don't use tone controls on the pre amp at all and I'm not inclined to. They are bypassed entirely.

I have the 2Ci, on their original metal stands (the ones with the T shaped foot). The quote below is taken from
https://www.stereophile.com/content/vandersteen-2c-loudspeaker-measurements
I drive them through other vintage, Harman-Kardon Citation 17s pre-amp and 16As amp, and original Monster cable - the ones the size of a garden hose. So I run tweeter +1 and midrange -1 as suggested below.

"I found a touch of lift in the high treble (tweeter set to +1dB) to be necessary to counteract the speaker's slight lack of off-axis air; this has to be balanced, however, against exaggerating the excess of HF energy above 10kHz. Though this might then be thought to leave the midrange a little depressed, I nevertheless found -1dB on the midrange control to give the optimal balance between the need for sufficient high-midrange energy and not to unduly emphasize the speaker's uneven response in the same region. This will be different for every listening environment and system, however. "