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
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