Sub Cable Effect

I've recently had a pair of relatively inexpensive IC's constructed for my single Rhythmic sub. These cables replace a pair of cheap Monster sub cables that I purchased for the initial placement of the sub. Cables run from amp pre-out with no return.

First listening sessions with these there was a noticeable increase in definition and quality of sound of the lower base. Nice, however, there was also a pronounced decrease in both the depth of the recording as well as the air or ambience about the instruments.

Technically, how is this possible when the only change is the sub cable? For discussion (if it matters) the cable is a 4-conductor, twisted quad Nirvana cable from Virtue Audio.

I've also noted the same negative aspects in the speaker cables that I've also had prepared - with a slight warming of the sound . . . not exactly to my liking; these an 8-conductor helix array.

Not giving up on them as there is always the potential that the cable's influence on the sound will change with additional 'burn-in'. And I wont' replace both at the same time in an effort to ID specific changes to the system.

I wouldn't have expected, but I prefer the Monster cable sub at this point, albeit not with that definition of the sound that this cable offers. As for the speaker cables, these are an upgrade to long runs of in-wall type HD 12 ga, 7 strand Cu . . . these have served reasonably well over time.

The system: VPI TT/Bryston CD - Plinius 9200 feeding Tyler D3M + DS12 sub.

Technically, how is this possible when the only change is the sub cable?

Sorry but there is no plausible technical explanation other than perhaps you reversed the phase or the previous connection was faulty or you changed something else like volume level or crossover setting (but forgot).
Wow - I just replaced my stock Rel cable for the Nordost baseline cable. The amount of low bass information is nothing short of amazing. Everything got so much better. Air - ambience - depth and sound stage is a world better. I would have to agree with Shadorne that maybe the phase is off (faster or slower cable could do that). Try moving you sub (if you don't have a phase switch on the sub) closer of farther to see if that helps. I did not have to change my phase but I did re-adjust the crossover lower by 2 hz and the gain down just 1 click.

My upgrade to the baseline also makes me wonder (I hate when that happens because it never comes cheap) what a better Nordost cable may do.
Funny, I had some very expensive IC's on my subs for awhile and then I put my Monster cheapo's back in after I sold them...looking to generate some cash and replace them with new sub cables. The Monsters go very deep, have great fullness and texture and blend my subs extremely well with my mains. I also replaced my $12500 speaker cables with monster M2.2s cables after a shootout with many potential high end brands loaned to me from the Cable Company. I also found some Monster Proline Mic cables that sound scary close to the best IC's I've ever owned or heard:O) Sometimes even us jaded audiophiles should eat some humble pie...we just might like it better than the Filet Mignon weve been buying over and over again:O)
There are some inexplicable things that provide better sound or lesser sound. No one can give you a definitive answer without testing, analyzing, and measuring with the proper equipment. You just have to go with what sounds best. It would be nice if this was different but it's not. I have 2 pair of the same inexpensive sub cables. As a test I sent one pair to a burn in service in order to compare the 2 pairs side by side. It will be interesting to hear the difference.