For me, using Synology Assistant doesn't work with the XPEnology releases (at least not for DS3612xs_3202 which I've tested). What I had to do is figure out what IP address had been assigned from my DHCP server and then navigate directly to that IP address in a web browser and set it up that way.
But the primary problem you're going to have, I think, is that the bnx2 driver isn't included in that release. But you don't need to reinvent the wheel, you just need to compile that module and add it to the image. An added wrinkle, though, is I think that driver requires external firmware so you'll need to make sure you get that loaded too. So you do have some work to do there. I've already got the dev environment set up, so I'll attach the drivers and firmware you'll need to this post. I haven't tested it so I don't know what you'll need to do to get the software to load the driver automatically.
One other thing I'm not clear about that you may want to consider yourself is that while the Synology kernel and most of the other stuff I seen in the package appear to be covered by licenses that allow you to use them (as most are based on GPLed code or similar and Synology has released the source code) I'm not actually sure that this applies to *everything* that's included by the XPEnology packages. I haven't seen anything definitive on this site that addresses that issue so I'm not sure if we can use everything in the package without some sort of license from Synology. Unfortunately, I don't see any way to buy a software license on their site.
Carl