Mostly the no warranty support is quite risky. In the UK, HD800s have the Orpheus 10 year warranty in comparison. Sennheiser EU support is also really great - my earpads had some deformity, and they sent me brand new replacements for free after I emailed them no questions asked. If I was in the US though and didn't have HD800s already, I'd definitely try to get in on this.
I see people online saying the HD800S has a 10 year warranty but that's not what the Sennheiser site says:
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https://portal.sennheiser.co.uk/rma/repairs/high-end
Sennheiser products are covered by a warranty for two years from the original date of purchase. The warranty terms and conditions can be found here.
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When you go to buy them it says they're offering an extra year. Where did you read about the 10 year warranty?