Interesting...I just went thru the manual, and while I was led to believe that the 1/4" outs were balanced, they are in fact 1/4" TS, which is a tad annoying. But there ARE ways to fix that...
Method #1 - Do it in software. Check this: https://www.kvraudio.com/product/doffset-by-wire-grind I use this whenever some sort of DC offset manages to sneak into things in Ableton, and it should be easy enough to track through this plugin to strip any DC before it gets into monitoring.
Method #2 - Do it in hardware. A couple of these little Lehle boxes that are made just for this purpose will fix the DC offset: https://www.amazon.com/Lehle-DC-Filter-Removes-DC-Offset-Voltages/dp/B00KTEZ1O2/ref=sr_1_1?dchild=1&keywords=dc+offset&qid=1625881768&s=musical-instruments&sr=1-1
Method #3 - Void your warranty. It's a pretty simple modification to add a pair of 1/4" TRS jacks, and by "dead bugging" a pair of audio transformers onto these and putting this inline after the 3.5mm outputs (you DO want to keep these DC coupled in case you want to use the 2600 as a complex modulation source). The manual states that these two sets of outputs are paralleled, so this would be the correct method for this mod.
For the present, my needs are being served by WireGrind's Doffset VST if/when there's a DC issue. But if I were to take this out for live work, I'd want to either have a pair of the Lehle filters in hand, or I could just as easily hand this to my local tech to refit the 1/4" outs. Same time, though, having used the ARP 2600 for as long as I have, you get a good eye as to which settings have the potential for DC issues, and you try and avoid that in a number of different ways.