Yes, the stereo one based on the specs you posted does look way under powered versus the other 2. 60 wpc @ 4 ohms will be less at 8 ohms.
If you're 50/50 music/movies and all ready have the center, I'd continue to use it. Center is most important channel in HT.
Personally, I'd recommend Yamaha, Denon or Marantz over Onkyo. You could check out accessories for less - they have factory refurbished units for pretty good prices.
https://www.accessories4less.com/mak...ceivers/2.html
You could likely find one that suits your needs for 400-500, and then pick up a Rythmik L12 or LV12F for around 600.