If I get it right I will need:

RS 232 splitter to connect the first Slimline RGB and
RJ 45 to connect the second splitter to the first splitter and the second Slimline RGB on this splitter.

This means that the first Slimline RGB will be on channels 5-7 and the second on on channels 13-15 (by setting the dip switch on the dimmer) so I can even dim them undependably.

Correct?

Can I do the same but using 2 RS232 splitters? Will this set up also work?