PSW-50 Setup Question

I currently have a RM5400 system that came with a PSW-50 subwoofer. At the time I bought the system, Polk tech support recommended running the front left and right speaker outputs to the speaker level in on the sub, then from the speaker out on the sub to the front speakers.

I was instructed to set the receiver setting for the subwoofer to "No". The receiver (Onkyo 656) then sets the fronts to "large" automatically, and will not alow the selection of small. This results in full signal being sent to the sub, including the low frequency bass. The sub then handles the lows, and the truly small speakers that are the front speakers handle the rest. This has worked well up to now.

I am interested in upgrading the front speakers to bigger, more capable bookshelf speakers. I have ordered the RTi4 speakers to replace the RM2000ii fronts in my system.

My question is, if I continue to use the speaker level inputs to the sub, with the RTi4s connected to the speaker level outs from the sub, what frequencies are passed on to the fronts? I have not found any answer in the manual I have nor while during web searches. Does the sub only pass signals above a certain level to the fronts in this setup (and if so, what is the lowest frequency passed along to the fronts) or does it pass everything along?

I want to make sure that the RTi4 speakers are only being passed frequencies that they can handle without being damaged (most important), and that the full capabilities of the better RTi4 are able to be used. Since the new speakers can handle much lower frequencies than the old ones, it would be nice to use this cacpability. Clearly, it cannot handle the really low frequencies that can be produced in many movies, however, and it is not truly a "large" speaker.

I was told previously that the RM2000ii speakers would not be damaged by this setup, but I don't know if that is because the sub only passes certain frequencies on, or if the speakers somehow only try to reproduce the frequencies it is capable of and filter out the rest somehow.

Do speakers typically limit themselves to what they can handle with some sort of internal device, or does some other device, like the sub in this case (or an amp or receiver) have to do this for them? In other words, is it safe to use this setup with the new speakers.

I would like to leave things as is if possible, since the wiring to the sub and the fronts is kind of built in, and it would not be easy to reconfigure. I would like to just swap the new speakers in place of the old, with no other changes if possible and adviseable.

Thanks for any help you can provide.