Since I don't know of any Mini DVI to HDMI adapters, I might be not the best help.
Have you looked at Monoprice.com yet for such cables?
And as there are too many Magnavox models for me to check all their specs, I guess all of them have HDMI inputs.
Why not use that input instead of the HDMI to Component adapter cable, which you linked to
here. Strangely enough they mention audio on that article too, but that would not work, as Mini DVI does not support audio transmissions and the colours on that adapter (Red, Green and Blue - RGB) don't match audio RCA cables (red and white/black).
Anyway, that HDMI to Component adapter cable will probably not work since those Maganavox TVs have no Component input (again, too many models for me to check them all, thus I only looked at
one).
Maybe have a good look at that guide I linked to and at the manual your TV came with, if the Mini DVI to HDMI adapter and a HDMI cable and the HDMI input of your unknown TV does not work.