Ive had a pair of ML ESLs for a few years now... No problems... The panels crossover to the woofer at 500Hz... And the woofer goes down to 42Hz... I would set your AVR to a full range and cross over the subwoofer itself at around 52Hz... So if you are doing a "small speaker" crossover in your AVR your most likely doing things wrong... You can try to run the ESL at another ohm setting via your AVR 2, 4, 6 or 8 and see how that changes your thermal issues or add a 2 channel Amp... These ESLs will test your AVR or AMP diving into low ohm territory... Standard AVRs and AMPs will want to double power as ohms half and ESLs "map" opposite of standard speakers... Are you bi-amping or bi-wiring??? Sounds odd to me if you are driving it all from an AVR... If I were to bi-amp I would use tubes for the panel and solid state to drive the woofer...
BTY you can vacuum the dust off the panels... RTFM...