How long is too long for interconnects?

Good advice so far.
XLR's for equipment supporting the AES Balanced standard is the way to go.-Cable coloration is minimized as a result.
12' for speaker cables will introduce more cable coloration than shorter lengths. So, you might want to demo a few different brands, if you are serious about sound.
B

Balanced/XLR is better than otherwise, certainly best chance of noise rejection.

Of course, your simplest choice is to run speaker cables that long.

@erik_squires But I always heard (or maybe misheard) that longer speaker cables were a bad idea.

There have been a number of threads here in the past on the question of long interconnects/short speaker cables vs. short interconnects/long speaker cables. My perception is that a majority favor long interconnects/short speaker cables. But as with many things in audio it depends on the specific equipment and the specific cables.

Generally speaking the following factors tend to reduce the criticality of interconnect cable length:

-- Low output impedance of the component driving the cable.
-- Use of balanced interconnections.
-- Low cable capacitance per unit length.
-- Insensitivity of the interconnected components to ground loop effects (which is generally not predictable).

Generally speaking the following factors tend to reduce the criticality of speaker cable length:

-- High speaker impedance.
-- Low cable inductance per unit length.
-- Low cable resistance per unit length.
-- Avoiding cables having unusually high capacitance per unit length, as that could have adverse effects on some amplifiers.
-- Low or no global feedback in the amplifier driving the cable, as noise picked up in a long speaker cable might otherwise be injected into the feedback loop of the amp, with unpredictable sonic consequences.

In this case, without knowing anything about the OP’s equipment I would say that it is probable that 12 foot interconnects will not be a problem.

Also, I agree with the earlier poster that there is no need to keep the lengths of the two cables the same. Unless, that is, you (the OP) envision the possibility of selling them at some point in the future, as unequal lengths would tend to turn off some potential buyers.

Regards,
-- Al

But I always heard (or maybe misheard) that longer speaker cables were a bad idea.

Kind of depends on a lot of factors. I mean, ideally everything is close together, cables never cross, blah blah blah.

The big issue among audiophiles is the big-ass very expensive speaker cables. If you are going to spend $300/ft for speaker cables, but $30/ft for interconnects, the latter is preferable.

I used to work in a theater and we had up to 150' from amps to speakers. Worked fine. Was it ideal? We could have put the amps behind the screen, but then we'd have 150' of signal cable, which, even when balanced, is MUCH more prone to noise pickup than speaker cables. And I don't mean your reviewer sitting at home with a glass of wine type of splitting hairs about blackest black backgrounds, i mean NOISE!!!

So, honestly, think about the subtle 'notes' you may change with longer amp cables vs. convenience of wiring the whole thing.

Best,

E