I’m using an A101 hooked via a crossover cable to an Adtran TA750 with 8 fxo channels and 16 fxs channels as a test bed.
The FXO channels on the 750 (1175407L2) were playing AM radio stations at an annoyingly loud volume until I installed simple DSL filters in-line. Now, I don’t hear even the slightest hint of radio frequency interference.
I’m using Excelsus Z-200SM Z-BLOCKER DSL filters but I’d imagine any similar low-pass filter would work. Try this before you send Adtran money for the updated FXO quad units that have RF filters built in.