The pair said they had exceeded their own expectations after scoring a second number one with their second duet album Together Again.
They continued their celebrations by stepping out into the brisk November air for the ITV gala at the London Palladium on Thursday.
Olivier Award winner Ball, 55, told the Press Association: "We didn't expect it.
"We were just mates, we thought it would be a fun idea to do some concerts, it turned into a first album, then it turned into a second album, and we are loving it."
Asked what would be coming next, he joked: "Hollywood I think, we're not ambitious.
"A musical of Downton is a really good idea - you heard it here first.
"I would be his Lordship and you (Boe) would be downstairs in the servants' quarters."
He broke into song as he added: "You would run the bath, come in with a drink and say, 'Good morning my lord, here is your breakfast'."
Less impressed with the casting idea, renowned tenor Boe, 44, replied: "No way. I would put sand in your bath."
He suggested instead an adaptation of the ITV jungle-based reality show: "I'm A Musical Celebrity... Get Me Out Of Here!"
The pair's success with their latest record - a collection of songs from much-loved productions such as Hamilton and West Side Story - marks a difference from the usual pop genre chart-toppers.
"Music is music and there are only two types: good and bad," Ball said.