I'll look a bit into this later this evening. But afaics the touchscreen does not get classified as a touchscreen, but as a mouse, hence it doesn't show up as touchscreen.
Some googling suggests the Intellitouch 2700 series, being apparently a rather old product, uses controller chips which do not support the industry standard USB-HID multitouch protocol, but something ELO proprietary, so they are not supported by standard USB touchscreen drivers and will need special treatment. Probably your touchscreen literally tells the OS "I'm a mouse, treat me like that.", so it works for driving the mouse pointer, but nothing else. There may exist special drivers or config to fix this, or one could use the advanced mouse support of Linux KbQueue interface to get at least single-touch input from that ELO screen, although it would make for awkward coding if you need different non-touch-screen code to handle the ELO vs. the other touch screen(s).
Anyway, need to look a bit closer and don't have time in the next hours.
However, that clock resolution message suggests some timing weirdness on your system. Also with the NVidia proprietary graphics driver it will be impossible to get high precision visual stimulus timestamping to work on your setup with dual-NVidia ie. for more than 4 displays, and getting it to work on 4 displays might be near-impossible or at least painful to set up, so i hope for you that millisecond or frame-accurate visual timing won't matter to your paradigm.
For this kind of setup - just as for any other demanding setup - i strongly recommend suitable AMD graphics cards with their well designed open-source drivers and the abiity to driver up to six displays simultaneously without compromising timing or other hacks, unless there is a strong reason to choose NVidia -- the only one i can think of atm. is if one needs CUDA compute ability.
-mario