After beating the final boss, go follow the emails, get the item, go to the satellite and a cut scene will trigger. Go get the Alternate dimension beat Apollo Flame then go beat "La Mu Xa" (Cause if you can't beat Apollo you can't beat La Mu Xa) After beating La mu xa youll get an email from Solo challenging you to a fight*. AFTER another fight with La mu.
But before that I HIGHLY recommend you become Tribe King AND Megaman Rouge. (Its on several other websites)
After beating Mu youll wake up still in wave form and infront of Rouge (Not Solo. ROUGE).
* Only after you get the stars on the continue screen I think.