I purchased speakers and amp through Best Buy which is being fulfilled by Ultra Discounts Corp

Sounds like this Ultra Discount Corp is able to purchase from BestBuy at a discount for their clients. If l’m correct the warranty is still valid just the same as if you bought your  Sonos via a professional installer. 

However, I suggest you call Sonos Sales for a definitive answer. 

Honestly, I’d be contacting Best Buy, or Ultra Discount, and not Sonos. 

Return policy is likely different.

How much did you save over buying direct from Sonos? 

Based on my (not recent) experience with Best Buy, check your manufacturing dates to make sure you aren't getting old versions that may have been improperly stored for many months.