No, the Bow will not benefit from other equipment which gives the Additional Attack special rule, like XHW. It will benefit from things that directly effect the A characteristic, like Savage Beast of Horros.
Shas'O Dorian wrote:Attacks refers to melee attacks and will not effect shooting at all.
The number of shots is printed in the weapon entry & is increased via the "Multiple shots (X)" rule.
The Bow of Avalorn does reference the Attack characteristic however.