Only the tweeters from your two front main speakers should be checked in.
Like Jostenmeat and Adam already suggested, set your Onkyo TX-SR805 receiver to a maximum master volume level, as indicated by Adam with the exact page of your 805's manual.
* Now your speakers; the ones to really check for, would be your two front main ones,
"their tweeters".
-> Very easy to verify: Put a CD, and put your ear right against the grille of your speaker,
right where the tweeter is. You'll know right away.
~ If you're not too experimented with this, just put the 805 in Dolby Pro Logic II audio mode,
and do that with your center speaker (put your ear right across the tweeter),
then do the same with your two front main speakers.
You'll know if one of the tweeters is caput.
The mid-woofs and the woofers are fine.
*** The tweeters for your center and surround speakers should be fine, no problem there.
* Kiss your son, and tell him that you still love him.

[It has to be a son, girls are not into electronics in general.]
Cheers,
Bob