Bi-Wiring with different lenghts?

The set-up you describe could limit the imaging of sound. If you don't notice it, don't worry about it!

I have a tri-wired setup and recently demoed some 10' biwires which were connected to my mids and tweeters while 6' was wired to the woofer. I could not detect any anomolies.

Digital, altho the very-minor negative effect of running different lengths to the 2 parts of the speaker would be inaudible to most of us, I suppose some top-1%-golden-eared 'audiofreak' could hear it...but if it sounds better to you, live it up!

BTW, if you can hear an improvement with your quicky lash-up cabling, probably you could hear even more improvement by using high-quality cable more suited to each 'end' of the speaker. I sure heard the improvement with my 2-ways.

Are the S5.3s 2-way? Three-way? If the latter, hi or low crossover?
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They are a two way system with the following particulars:

Bass/Midrange
Driver: Two 5.25" rigid poly fiber cone,die cast magnesium baskets.

Tweeter: 1.125" double chamber, silk dome

Crossover: 2.4 kHz@18 dB/octave.

The cables I am using actually are the result of some searching. I find the Lat-1000SSD's to have wonderful imaging and are extremely well defined in the high frequencies. They also have very articulate but a bit lean midrange presentation but have never been the last word in bass. I am using the Lats for the high connections.

The Custom House Barracudas, which I am using for the low freq. connections, on the other hand have a very warm and full midrange presence and an expansive deep articulate bottom end.

So far the result of pairing the two in this manner is pretty pleasing. The test of time is yet to be measured of course!