Dave, I'm not familiar with the POD XT but I do know my UX2!
You should be able to permanently hook up your TonePort and use that as your soundcard - it's got some well written ASIO drivers that, coupled with Line 6's 'ToneDirect' monitoring mean you should be able to record with unnoticable latency.
Then you can forget all about your Soundblaster
BTW, it's likely a mismatched sample rate (in the SB card) that's causing your playback woes.
Unplug your POD and then try opening GearBox with the TonePort plugged into a USB port (
not a hub) and see if it recognises it. If it does, you're in business and you can disable the SB card, however, you'll have to hook up some speakers to the TonePort for playback.
Next step will be to set up GT3 to recognise the TonePort using the Options>Audio menu; if you get this far, you'll be cooking on gas Dave!
If you need any help along the way - post back, you know where we are!!
Steve