20 dB headroom considers the worst case headroom required on some classical pieces. For rock/pop, headroom rarely exceeds 12 to 14 db, for instance. The amp is rated for 70W/ch at 6 ohms. As i mentioned on my earlier comment, it would take 60W/channel on my 6 ohm speakers to run at 80db (with 20 db headroom included, i.e., run it at 100 dB). Is it still risky?
You made a good point, I was too focussed on classical. For most other genres 80 dB average 95 dB peaks seem reasonable. It is worth trying.
For me I won't spend $500 on anything that does not have pre-outs but that's just me.. For 2 channel digital source only, the WXA is a much better value than the A-S801 imo.