Luton have signed former Peterborough and Brighton striker Craig Mackail-Smith on a two-year deal.
Norwich City have completed the signing of goalkeeper Jake Kean following his release from Blackburn Rovers.
Espinoza caught the eye of European scouts over the summer after impressing for Honduras at the 2012 Olympics.
Wigan were credited with holding an interest at that time, but were unable to put a deal in place.
They have, however, refused to accept defeat in their pursuit of Espinoza and the 26-year-old should complete a switch to England once the January transfer window opens for business.
"He called and told me that he's basically decided that he's going to Wigan," Sporting KC manager Peter Vermes told the Kansas City Star.
"It was a tough decision for him, but it's something that he wanted to do. He wanted a chance to play in the English Premier League, but he also wanted to thank me and the club for everything."
Vermes added: "I told him I really appreciated his commitment to the club.
"He's been a great guy on and off the field for us for several years. His growth as a player has been tremendous. I told him we're happy for him, but that the doors are open if things change in the future."