I'm not positive, but I don't think you'll get Poweragent to detect your Garmin. You might be able to import your .fit files per hand, though.
If that doesn't work, try golden cheetah
. That will work with your Garmin and might give you a file format that will be supported by Poweragent.
GC is a definetly worth a look anyways, it gives you pretty good functionality and it's free.
I still find WKO+ a little bit more intuitive and customizable, but that might be because that's what I'm used to the most. I'd recommend seeing if you can't fullfil your analyzing needs with Poweragent and/or GC first.
"Nothing compares to the simple pleasures of a bike ride," said John F. Kennedy, a man who had the pleasure of Marilyn Monroe.