Art isn't listed in AA's specialty items, but either way you're beyond the limit per the website:
Rules, exceptions and packing instructions apply to special items. The maximum weight and size for all items is 100 lbs / 45 kgs (some exceptions apply) and 126 in / 320 cm (length + width + height). If your equipment exceeds allowances, contact a freight forwarder. All bag fees are non-refundable and apply per person, each way. Overweight and/or oversize charges may apply.
https://www.aa.com/i18n/travel-info/...and-sports.jsp
We don't accept checked bags over 126 in / 320 cm.
https://www.aa.com/i18n/travel-info/...ht-baggage.jsp
8'x6'x6" (not including addt'l inches for the box and packing materials to safely hold it) would be beyond 126".
That said, I would assume the baggage handlers wouldn't take that much care in packing it either way and think it would be safer using a professional shipping company with shipping insurance.