Sorry, not quite correct. You're confusing layers of the OSI model.
Standards with multiple lanes - which includes the 4-lane 10GbE standards - split the signals at the physical layer and then reconstitute them at the physical layer.
Say, for example, that you had 10Gbit of data coming into your XAUI-based 10GbE NIC. The 10GbE silicon would split the data stream (which it sees as a stream of 1s and 0s, not at packets) into 4 lanes of traffic and fire them out to the interface.
The interface would then either dump the signals onto copper as radio waves (each lane being it's own chunk of spectrum) or forward these to an optical transceiver. If sent via copper then the interface and silicon on the receiving end need to be able speak the same number of lanes with the same kind of encoding. So if you are using XAUI you are probably using 10Gbase-CX4 as your copper medium, for example, and you'll need some silicon somewhere in there that can pick up the 4 lanes of traffic emitted and put that back into a single 10Gbit stream that gets dumped onto the PCIe bus.
If, however, there are optical transceivers in play this is different again. The optical transceiver will take the data stream it gets (4 lane, 10 lane or just one lane) and convert that into light according to the standard it is designed for. This may mean that a 10Gbit stream from the application layer is broken into 4 2.5Gbit streams at the NIC silicon then reconstituted into a single 10Gbit optical stream that then goes through the same process in reverse.
It's also equally possible that your single 10Gbit stream goes from application layer all the way to the transceiver as a single 10Gbit stream, but the transceiver then cuts it into 100 different colours before firing down the fiber.
When optical transceivers are involved the general rule of thumb (that doesn't always apply, but let's ignore that for a moment) is that if you have two optical transceivers that speak the same optical standard they can communicate with one another, regardless of the underlying silicon/copper signal architecture. If, however, you are trying to connect using copper (I.E. forgoing the use of expensive transceiver hardware) then you can only connect up nodes if the underlying silicon can understand one another.
Hope that helps.