The speaker level spring terminals on the polk sub are essentially a pass through with a tap to receive the signal. The polk will contribute an insignificant load to the amplifier. The speaker level output passes what is coming in to the input side, it does not high pass the signal at the crossover frequency, so whatever you hook to the polk will still be run full range.
So yes, you can run speaker wire from the amplifier to the polk, and from the polk to the horns. Just be careful how you configure the horns in series or parallel, and if you add the sony into the mix. Those little amplifiers don't make a lot of current, so if you go much below 8ohms it will just activate the protection circuit. You might get away with 6ohms, 4ohms is not likely. You can always add a resister to the circuit if necessary at the wattage you are dealing with.
Another option is to get a line level converter, it takes the speaker level as input changes it to line level RCA output, then you can use an amplifier of your choice. They are about $10.
Just a side note 2W may be enough for the horns, but it doesn't allow for really any dynamic headroom, you may end up with clipping and find music to sound a bit flat without more reserve.
BTW, I would LOVE to have something like your previous system!
