I have 2 subs, with only 1 sub pre out. HELP

You need to have both subs hooked up and running for Audyssey to measure and create a meaningful EQ file.

There are no cons to running a splitter. Split at the AVR subwoofer pre-out and patch cord the "Y" splitter over to your sub. I use Mediabridge splitters and cables as to me, for the delivered ten dollar price tag, they're quality made, good looking cables.

Mediabridge RCA "Y" splitter cable.

Mediabridge RCA subwoofer cable: 15'.

Y cable is fine but take a few moments to balance the output of the 2 subs before you run Audyssey.

For clarification purposes, just adding to Kal's above, use a sound level meter to gain match each of the sub's output at one foot equally (measuring each sub while only the sub being measured is turned on) so the output of both subs, when both subs are powered on, at the MLP, measures a combined 72dB - 75dB. This should be done before running Audyssey.

The psw 111 is an 8" sub that Polk specifies with a -3 dB point of 42 Hz.:
http://www.polkaudio.com/products/psw111

The psw 505 is a 12" sub with a -3 dB point of 28 Hz:
http://www.polkaudio.com/products/psw505

The difference in extension between these 2 subs is the better part of one full octave. We don't know the max output differences, but I think it's safe to assume that the 505 will have significantly more output across the range than the 111. Therefore, if you try to use them together, the 111 will always be the limiting factor, and you'll never realize the full potential of the 505. Th 111 will compress and distort long before you get to the full potential of the 505

If you really want to use them together, I suggest you use the Geddes technique for setting up multiple disparate subwoofers: http://mehlau.net/audio/multisub_geddes/ The technique sets the sub with the lower limits to a lower level and allows more headroom from the stronger sub. The technique does require measurement capability.

Another approach would be to use the smaller sub as a "mid-bass module" or MBM. However, this requires that you send the MBM a different signal than the deep-bass subwoofer. That requires an external crossover like a Behringer crossover http://www.behringer.com/EN/Products/DCX2496.aspx You set a high pass on the MBM and a low pass on the deep bass sub.

If neither of those solutions work for you, then I suggest you find another use for the 111 and consider getting another 505.

Good luck.

Craig

That technique works great for identical subs. For non-identical subs, with vastly different gain structures, not so much.

Craig