Helm, who was an unrestricted free agent, signed a one-year contract July 29. The 34-year-old forward scored eight points (three goals, five assists) in 47 games for the Detroit Red Wings last season, his 14th with them.
"Just the team they've been building for the past couple years, I think they've got a great squad and I just want to be a part of it," Helm said Wednesday.
"It's a little bit of mixed emotions. I've been [in Detroit] for a long time, I raised a family here and I'm sure this will be home when we're done. But when I heard the news that everything had kind of happened, I was extremely excited. I'm really looking forward to playing with the Avs."
Selected by Detroit in the fifth round (No. 132) of the 2005 NHL Draft, Helm has scored 251 points (112 goals, 139 assists) in 744 regular-season games and 21 points (11 goals, 10 assists) in 82 Stanley Cup Playoff games. He won the Stanley Cup with the Red Wings in 2008.
"Darren is a high-energy, competitive player who brings veteran leadership to our team," Avalanche general manager Joe Sakic said. "He helps our depth up front, is good on face-offs and is an effective penalty killer. Darren is a Stanley Cup champion who will be a great addition to our dressing room."
Jost, who was a restricted free agent, signed a two-year contract July 30. The 23-year-old center scored 17 points (seven goals, 10 assists) in 54 regular-season games for the Avalanche last season and four points (two goals, two assists) in 10 playoff games.
"Tyson took a big step last year and was a key contributor to our team," Sakic said. "He has worked hard to improve his game and earn a spot in our lineup. Tyson is a guy with a lot of character who competes at a high level day in and day out. We are excited to have him under contract for another two seasons."
Selected by Colorado with the No. 10 pick in the 2016 NHL Draft, Jost has scored 89 points (39 goals, 50 assists) in 262 regular-season games and 10 points (six goals, four assists) in 40 playoff games.
NHL.com independent correspondent Rick Sadowski contributed to this report
