It's a confusing subject, no question. There is a theory that says that a high quality DAC will be able to equal out even the worst $50 Walmart DVD player with a $60K Burmester transport. I do not agree with that assertion because I haven't experienced it to be true. The transport still matters, otherwise there would be no reason for these converters to exist. Why spend hundreds of dollars on a USB to S/Pdif converter when optical digital straight from the motherboard will do the job? Further, why would there be any difference between optical and coaxial? Even if we accept that optical would produce higher incoming jitter, if the DAC is supposed to be able to eliminate that, then the medium shouldn't matter. There'd be no need for glass fiber cables either, what's a little more jitter from an acrylic cable?
I can't answer the question of whether the Jkenny Hiface or the Audiophilleo with battery is better, I haven't heard either. The only way to answer that is to try them both. I can say however that using a motherboard USB port is far from ideal. Whether you want to use the AQVOX supply, or the SoTM card, or just a powered USB hub, it seems that anything is better than USB straight off the motherboard. I won't even get in to USB cables.
I do think that a computer can be a truly high-end transport, but it has to be done right. If you just want to buy something ready to go there are models like the Sonore servers, or you can DIY.