A few questions for writing a driver

I recently purchased the USB-UIRT to use with my Mac. It appears there are no Mac drivers available so I'm writing my own app to communicate with it. Eventually, I hope to have an app that makes the UIRT available as a network socket.
So far I've been able to communicate with the UIRT and to send it commands and read the results (set IR mode, get ver., get IR sequences, etc.).
I have encountered three issues so far:
1. USB reads are always preceded by the two bytes 0x91 0x60 or 0x81 0x60. It appears 0x91 0x60 is used for terminal data while 0x81 0x60 for non-terminal data. I did not see any reference to this in the documentation, is this correct?
2. USB reads always return immediately even if there is no data (i.e. I just get 0x91 0x60). Is this the expected behavior?
3. I can set the mode to UIR or RAW (I get 0x91 0x60 0x21 as confirmation) and the requisite IR codes. However, when I try to set it to RAW2 (mode 0x24), I get the confirmation but get no IR codes. Also, the red LED does not light up when I fire a remote in its direction. Is there something different that needs to be done for this mode to operate correctly (DTR, RTS, etc.?)
The firmware info block is:
09 05 01 01 1A 03 04
Help is much appreciated!
So far I've been able to communicate with the UIRT and to send it commands and read the results (set IR mode, get ver., get IR sequences, etc.).
I have encountered three issues so far:
1. USB reads are always preceded by the two bytes 0x91 0x60 or 0x81 0x60. It appears 0x91 0x60 is used for terminal data while 0x81 0x60 for non-terminal data. I did not see any reference to this in the documentation, is this correct?
2. USB reads always return immediately even if there is no data (i.e. I just get 0x91 0x60). Is this the expected behavior?
3. I can set the mode to UIR or RAW (I get 0x91 0x60 0x21 as confirmation) and the requisite IR codes. However, when I try to set it to RAW2 (mode 0x24), I get the confirmation but get no IR codes. Also, the red LED does not light up when I fire a remote in its direction. Is there something different that needs to be done for this mode to operate correctly (DTR, RTS, etc.?)
The firmware info block is:
09 05 01 01 1A 03 04
Help is much appreciated!