I get the impression that when you start adding extra drivers, you may need a better/stronger source to get the most out of the higher end CIEM's. Is this correct and if so, is there a normal line where if the CIEM's have X number of drivers your probably going to need/want an amp/DAC/better source? I usually use my laptop or Creative Zen as a music source when when using headphones at work, on travel or when working out (at home I use speakers not headphones). If I upgrade to CIEM's, I would probably look at getting a better portable music player but may have to live with what I have for a while depending on how much the new CIEM's cost. It would kind of suck to spend $500 on headphones and not be able to get good sound out of them because my music player can provide enough umph to push the extra drivers.
In my experience this isn't necessarily true, it depends on the complexity of the crossover and some other factors. The JH16 is quite easy to drive for example while the ACS T1 will benefit more from an amp. There is a source matching section in all of my CIEM reviews which hopefully can give you a good idea of how the CIEM performs with various levels of sources.