Your sample rate rate and the USB extender data rates are two different things. The 1.5MB/s means that the converter does not support USB 2.0's high speed mode. If you're DAQ device operates using the USB 2.0 high speed mode, then the converter won't work.
I've not had the opportunity to test extender devices with NI DAQ USB devices, but I see no reason it can't be made to work. The USB to CAT5 extenders are maybe the worst choice for extending USB. Theoretically, they should work fine (USB 1.1 only), but all they are doing is transmitting the USB signals over CAT5 cable. It never enters the ethernet domain. If you pick up any noise, these extenders are likely to cause problems. Try keeping the bulk of the cable in the most electrically noise-free area of the installation.
Using USB hubs with 50m USB to CAT5 extenders is not allowed. The delays they add cause the communications path to exceed the USB's maximum allowed transmission delay.
Icron's Extreme USB devices impress me the most. They don't require additional software drivers and they fully meet the USB 2.0 specification. However, beware that they will add delay to the communications. I expect you will see that it takes twice as long to complete a USB transaction. If this is a problem, try an active cable which includes signal conditioning.
I hope this helps.
