Try multiPE and select the hostNIC script.
Q:My car does not start.How can I make it start?
A: Leave alone the car, use the motorcycle instead.
You are mixing together two different things.
In a Qemu there is a (virtual) built-in card which is (virtually) a Realtek 8139.
The LiveXP sees that card (and not the "real" network card, which coincidentally on your motherboard is also a Realtek).
See if this clears the matter:
Your LiveXP most probably contains a suitable driver for the QEMU (virtual) network card, but not one suitable for the "real" Realtek card on your motherboard.
See this (and links therein) for methods to either add the drivers to the build:
or loading them after having booted:
(a good idea could be to use the DriverImportPE to test, and then re-build with the drivers added)