Lance's response is correct. You cannot use metamagic on the highest level of spell your character is able to cast, because metamagic raises the magic required to cast that spell.
For example, Jaelle can cast all 9 levels of sorcerer spells. She also has maximize spell. When she casts maximized spells, she can cast levels 1-6 through maximized spells. Casting a 6th level spell at maximized level uses up one of my regular 9th level spells for that day. If she were a wizard, she would have to prepare it at 9th level, because 6+3=9 and maximize adds 3 spell levels to the casting requirement.
For a metamagic feat that added only one level, I would be able to cast level 1-8 spells with that type of maximize.
Because bards only have 6 levels of bard-specific spells, you would never be able to use maximize, empower, extend or any other metamagic feats on a level six spell because the requirement would be higher than the level you can cast.
Hope this helps,
~Carillon