yeah, its a large issue to my understanding depending on country… rather unfortunate… k702 are quite bass recessed compared to k712 which is the warmer more balanced sound but to be at $220 thats kind of nuts in my opinion.
zen can should be able to drive them without balanced port… zen dac can power them… but it has to be fully cranked though it loses some of the bass so its slightly too weak… Yes balancing them helps and is rather common. I would recommend asking one of the more tech savvy people on here about that… potentially on zen cans respective thread such as here 🔷 iFi Zen CAN Signature 6XX - #96 by theFritz which is just the drop version of the amp or make another thread asking about it just to be fully sure… you can also head to the dt 880 600 ohm forum on here and ask. 🔶 Beyerdynamic DT880 600Ω - #453 by Mufflertape
I would ask around some of the forum members here find someone from your area… for me I use Etsy though I am not sure if people from your country offer this service… you can also outright buy an 880 already modded on the used markets if you prefer… just takes some digging or placing up some ads for one.
you don’t need balanced for all headphones… it won’t make them sound spectacular it just makes fully utilization of the amp. K712 aren’t very needy on power to begin with at 62 ohms meanwhile the 880s can be 600 ohm… you also don’t even need 600 ohm 880s they just sound the best overall… you can be just fine with the 250 ohm version as well.