SP-16 can pass an incoming signal to the output. This is easy, just touch any track on the touch screen to open the TRACK MENU, then select TRACK TYPE as "THRU" and the SP16 will pass the audio through, and you can add effects to it, etc.
So yes, you can have a "chain" of RMX-1000 + SP-16 as a single "mega effect processor" in your mixer's send/return path.
Why would you put the RMX before the SP? Wouldn't you want to add RMX effects to whatever is coming out of the SP-16 (samples, loops)
Or is your goal to be able to run audio through the RMX, then occasionally sample that "effected" audio into SP-16?
In either configuration, you can do this, but every analog-to-digital conversion you perform adds a slight bit of latency to your signal. This is a long chain of devices and by the time the audio gets back into your DJ mixer, it may be verrrry slightly lagging behind the audio on your other channels. It may not be noticeable, but you'd have to find out.