You might have to move the Audiophile to a different PCI slot, if there's truly a resource conflict. But since you really don't need the onboard sound, this is a non-issue for you. On to latency.
The setting in the control panel is for the size of the DMA buffer. That's only part of the latency equation. 128 samples at 44.1 kHz is only 2.9 milliseconds. This is roughly equivalent to the time it takes sound to travel 3 feet. The actual latency you're experiencing is probably much worse than that, if it's affecting your ability to record.
The rest of the latency comes from your software's internal buffers. The software retrieves the samples from the DMA buffer, and places them into another buffer until it's ready to do whatever it's going to do with them (write to disk, add effects, etc.), in between screen redraws and other stuff that the software is doing. If the software doesn't empty the DMA buffer in time, you get a pop or click due to the discontinuity of the waveform. The time it takes for the software to process the samples and spit them out is added to the hardware latency to get your total system latency.
So, what to do? It may be possible to tweak some settings in the software to achieve lower latency, but I haven't been able to locate any documentation specific to your software, so you're kind of on your own there. But the best solution from the standpoint of minimizing latency for overdubs is to use the Audiophile's "zero-latency monitoring" feature.
First, you have to turn off any software monitoring that GTP is doing. Otherwise, you'll be getting a direct signal from the Audiophile, as well as the latent (delayed) signal from the software.
Then, go to the Delta control panel's "Patchbay/Router" page. Set the "HW Out 1/2" output (the RCA jacks) to get its signal from the Monitor Mixer. Then, on the "Monitor Mixer" page, your software's output will be on the "WavOut 1/2" faders. Make sure they're not muted, and bring them all the way up. Also make sure the Master fader is not muted, and is all the way up. Now, un-mute the "HW In 1/2" channels, and bring up their faders. You should be hearing the signal from your input, with no latency. The same signal should still be going to the software's inputs, as long as you have the right device selected. This could take some trial and error. But zero-latency monitoring is a very cool feature, so keep trying.
Are we there yet?
Don