Want to buy Ayre C-5xeMP but...

Yes

No matter how it is done at the end of the line is a digital to analog chip which almost always is designed to accept a serial protocol called I2S. Whether the transport is in the same box or we use an external transport or we use a computer at some point there is a receiver chip which takes whatever it is being fed and converts it to I2S for the DAC chip. That "whatever" could be ethernet, Toslink, SPDIF, USB, Firewire, etc.

From what I've read the problem with synchronous usb is it has to reclock the signal from the computer. Asynchronous usb apparently solves this problem. As of now the Wavelength Audio usb dacs and the new Ayre usb dac are the only ones that use asynchronous usb. Also Herman is right that usb 2 does support 24/192 data but there are no dacs that take advantage of that yet. Wavelength is working on it and will probably have it soon.

Any time you use a outboard dac the signal must be converted and reclocked with the exception of the asynchonous usb and dacs that can accept a I2S connection. As for firewire I'm not sure if it needs to reclock or not. Firewire does support 24/192 though. The Linn DS players have the dac inside and take the data straight from a buffer and don't need to reclock the signal. This is similar to a one box CD player. I am not a expert but this is how I understand it from what I have read online.

IMO using your own ears to decide what sounds best to you is more important a factor than any one technology.

Cheers,
Sean

I want to add that spidf, toslink, and synchronous usb conversion create more jitter than the other alternatives.

After a lot of thought I am really considering the Ayre DAC because of the Ayre sound and the asynchronous USB.

But, I am concerned about what I have been reading about how different USB cables affect the sound. Now I will have to play the cable game again.

How big of an effect can USB cables make on the sound?

Check out the Synergistic Research Tricon USB cable. One on sale now here.