Utility
The Volvo is a better choice than the A6 in terms of transporting cargo, especially if you frequently need to carry a lot of stuff or sizeable pets.
Neither the Audi A6 nor the Volvo S80 has a marked advantage regarding seating capacity.
Dimensions
The A6 is significantly more ponderous than the Volvo.
The Volvo S80 and the Audi A6 compete for the same parking spaces.
Convenience
The Audi's fuel tank will need to be replenished a tad more often than the unit in the Volvo S80.
Cost
The destination charge is a standard charge for transporting the vehicle from its point of origin to the dealer. It costs approximately the same to get the Volvo S80 to the dealership as the Audi A6.
There isn't much of a difference in gas mileage here, but if you must know, the S80 is slightly more economical than the Audi A6.
Producing an accurate fuel economy evaluation is so tricky that some think not even the federal government can do it, but it looks as though both the Volvo S80 and the Volvo S80 perform roughly comparably when it comes to gas mileage.
With respect to MSRP, the Audi costs significantly more than the S80.
The Audi A6 is significantly more expensive than the S80 as far as out-the-door cost.
Handling
The Audi and the Volvo S80 have approximately comparable tires.
Drivetrain
The Audi A6's engine is substantially more massive than the Volvo S80's. Keep in mind that bigger engines may use more gas than smaller ones.
The Volvo S80 has no lessons to learn as far as pickup from the Audi A6.
Comfort
The Audi A6 is not particularly roomier for your passengers than the Volvo S80.
Overview
The Volvo and the Audi A6 have the same basic after-sale protection.