The 25 mV was mainly due to my Kara preamp, not the Nilai amp. The Nilai amp by itself had 7 mV of DC offset when I first got it, which is low enough that it won't damage anything, and that was with the gain set to medium (12.3X) and nothing hooked up to the inputs.
I think the Nilai specs say DC offset should be less than 10 mV (should be at any gain setting), which mine was. So if you don't adjust anything it should be fine. I managed to adjust it down to zero mV, but I still had the 9 mV coming from the preamp when it was reconnected, and with the low gain setting on the Nilai this got turned into 25 mV DC at the speaker (the other speaker had about half that).
I sent an email to Hypex asking what their specs for DC offset were for their Nilai preamp kit, and if there was an adjustment or maybe some circuit to keep it low (servo, capacitor, etc). I haven't heard back from them yet.