From the press release issued by Icelandair Group:
https://newsclient.omxgroup.com/cdsP...ssageId=573040

A total of 16 Boeing 757 aircraft will be used to serve the company’s route network next summer, two more than in the current year.

Icelandair Group is a holding company with many aviation activities. Icelandair (the airline) is just one part. While Icelandair Group does own 767s, all Icelandair scheduled flying is done with 757s. From the Icelandair Group fleet page:

Icelandair operates a single type fleet of Boeing 757 aircraft in its international network. The type fits extremely well with Icelandair‘s route network. Also, a single-type fleet creates significant cost efficiency in terms of maintenance and training for crew and engineers. The Group invests considerably yearly in its fleet, in order to sustain and improve passengers‘ flight experience.

http://www.icelandairgroup.com/our-company/fleet/

Thus, all service to DEN will be with 757s