I have to keep emphasising that for electronics, the less you use it, doesn't mean that you will be able to keep it longer.
Surface mount capacitors don't last that long, so in some cases the electronics can last 10 years but in some unlucky cases, you get 6 years.
We tried to offer extended warranty a few years back but there is no taker. An integrated amp board is especially costly since the DAC board consist of the preamp and DAC. Then we have to ship the board by FedEx international to the service center. The service guy has to open the item, test it, order the parts, replace the board, test it again, pack and ship it back to you.
Ask for breakdown of the $400. The labor cost should be limited to $150 (our general agreement with the service guy) unless the repair is complex (certainly not in this case). I think the repair cost is very reasonable compare to other brands.
$400 service for 6 years = $66 per year, that's not that bad. My aircon has to be clean and service every 3 months that cost me $60 each time!