Subwoofer without sub-out port

Hello and good day! I have three receivers, and none have a sub-out port. The newest is a Yamaha R-N303 purchased this week. Also purchased a Polk PSW10 sub, is there any way I can use this fine speaker? Reading the manual there are two setups that don't use the sub out, one involving preamp out and the other (opt 2) using the speaker in and out clips on the sub. Info on audio forums indicate that one could go to the speaker in on the sub, then speaker out back to two other speakers, and this is shown on option two in manual. Will this work? I have called support??? three times and the nice people in Manila now nothing about the product.
I was told that if I did not have a sub-out port the speaker could not be used, yet clearly in option 2 there is no use of sub-out port. A look on the web shows that a receiver with speaker a and b front selections could use B to go to speaker level clips on sub. Another option mentioned was use of a line level device to convert receiver speaker output to low level RCA outputs. Sorry, this so long but seems that there is a lot of confusion about this issue. I would be so grateful for any info.
Baseless in Newberry, Fl