How important is it that all cables come from the same manufacturer?

Zero. Use the cable you need. it doesn't matter where it comes from.

If there’s a manufacturer who seems plugged into ur brain, go for it. But, I think once you trust your own ears it’s perfectly fine to mix n match. It all comes down to personal preference and system synergy. That takes experimentation and and trial n error. No one can advise u on that except you.  Me?  Acoustic Zen just sounds right without spending mega bucks.  But, I use an Apogee Wyde Eye digital cable because it seems to exhibit the same sound characteristics as my other AZ cables at a fraction of the cost. So, case in point.  Best of luck. 

Zero reason why one needs to go all one brand for cables 

I like to mix and match. However,there are some folks that love a certain house sound,and that’s what they like. I don’t think there is a wrong answer. Do what floats your sonic boat. 

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