Unfortunately the only solution is a new/refurbished power amp. Got mine fixed for $2k CAD (approx. $1300 amp + $500 installation, + tax) few months ago by local Lexus service in Canada, after a different audio shop failed to fix it. See attached photos for my old broken unit. Bubble wrap bag is from the new replacement unit
Buying them on eBay is cheaper, but may or might not be compatible with your vehicle model, trim, etc.
Good luck with your vehicle. Let us know if you find a different solution...