Most audio recording apps have some kind of option menu somewhere in the program itself that allows the user to determine which soundcard to use ( for comps that have multiple soundcards ) and at which rate you prefer to work with. I'm pretty certain that PT8 has that, and you should be able it tell by accessing it.

It's also possible that there are some loss issues with the DAC converters, as is often the case with some of the cheaper computer audio cards. Add that to a little more loss from using RCA to mini 1/8 inch jack connectors, and this may also be a contribuyor. Sometimes it is enough to make a rather discernible difference, in which case you likely would need a better card.

AJ