Best way to hook up dual sub-woofers

I recently purchased 2 NIB PSW505s by Polk audio at a ridiculuos low price and would like to know which is the best way to use both subs with my Onkyo 876. Do I need an external cross-over or the Y spitter would do the jobs?
Use a Y-splitter from the Onkyo, and set the subs up so that they are both the same distance from the listening area. The Audyssey MultEQ XT setup tool will then measure and tune them as one.

Make sure you do all 8 measurements with Audyssey.

Set the subwoofer crossovers as high as you can.

Dave, Do you mean that to leave the sub corss-over at 120hz while set the Onkyo internal cross-over at 80hz?
Yes....that way, the Onkyo crossover will be in control. Where you set the Onkyo X-over will depend on your main speakers?....I use 80hz with my speakers.

If your main speakers are very small, and have little bass may need to set the crossover point higher?

Regarding Audyssey MultEQ XT setup....I bought a cheap MIC stand with boom adjustment. I got very good results after getting the hang of it (two large VMPS passive subwoofers).

Good idea to read this over:

I've found the best way to connect subs is using speaker-level connections if the subs allow for it.
Dave, good info. Thank you. Off the topics, I have listened to my friend's Duetta and they were hook up with a Classe amp with AR pre. I could actually SEE the music. The Apogee is amazing with properly set up.
I second Dave's suggestion.