Here's my new best estimate after the Hossa signing ... the Red Wings' cap number for next season is a little more than $53.2 million. The league salary cap is $56.7 million.
That leaves about $3.5 million this season to sign Valtteri Filppula and Chris Chelios, assuming Jimmy Howard will be in Grand Rapids and his salary won't count against the cap. So that's more than enough room to sign both Fil and Cheli.
Next season becomes the issue when Henrik Zetterberg gets a more than $5 million raise and Johan Franzen has to be signed as well.
Of course if the cap goes up more next season, perhaps Hossa could be signed if ... ah, forget the numbers and let's just fantasize about the upcoming season for a bit.