Connect the amp's speaker outputs to the sub's high-level input? Should be no problem. The voltage in the amp's speaker outputs is the same whether the amp's power supply is 220V or 110V. On top of that, you are feeding your amp 110V anyway, via the stepdown transformer.
But watch out for those Internet audio forums--you never know who's advising you. ;o)
But watch out for those Internet audio forums--you never know who's advising you. ;o)