Hi Shaq,
I own a Lynx 2B sound card, a couple of outboard DACs, as well as Avalon Opus speakers. Regarding the Lynx with the Eidolons, unless you are running some tubes somewhere in the chain to fill out the sound, I would be worried that the Lynx would not be a good fit. While the Lynx is a good performer as a sound card, the Eidolon's are so transparent that all of the problems inherent in the PC (noise, power supply, environment), combined with the fact that the Lynx is designed with the accuracy needed for mastering in mind, will most likely result in some glare and thinness. The Lynx fits in very well on some systems and sounds very similar to the Benchmark DAC 1, but in my opinion neither of these are an enjoyable combo with Avalon speakers.
My favorite affordable DAC is currently the MHDT Labs Havana, but it is not ideal when driven via USB. If you really want to go USB, you might consider looking into some of the Wavelength products, but they can be quite expensive.
Alan