Computer output to DAC, which route?

It is difficult to compare USB to Firewire since Firewire is expansion bus while USB is peripheral bus. Firewire speed is guaranted while USB speed is much lower than rated because it runs under protocol. 480Mb/s rated USB 2.0 runs at about half of this speed while Firewire 400 runs at full 400Mb/s (for the reason of guaranteed bandwidth is widely used in broadcasting industry). In addition Firewire does not engage main CPU having own processing unit with DMA ability. For that reason it was removed from Ipod since it posed security risk. Bringing device with Firewire to work might allow to bypass passwords (Direct Memory Access) and plant virus or spyware on the system or to steal company secrets. Big companies would most likely prohibit Ipod as security risk and that would be disaster for Apple. One thing that killed Firewire on (IBM) PC was greed. Apple charged $1 per port for royalties and that's a lot in very competitive business.

I'm not even sure how important speed is since 16/44.1 requires only 1.4Mb/s. Asynchronous operation might be a different story - don't know much about it.

One test for the future will be HDTV. Firewire 3200 could deliver (with 3% overhead) about 3100Mb/s bandwidth - not enough for 1920x1200 at 60Hz. What about Thunderbolt that has about twice the bandwidth of USB 3.0 and is likely to migrate to (IBM) PC ?

I am just starting to look into this. My constraints are a PC running Windows or Linux, listening through old Stax headphones connected to an integrated amp a couple feet away from the computer, and very low budget, say, around $200. By the way, all my PCs (purposely) have FireWire on the motherboard, and I do have an old D/A converter I can use to get started. I would be looking to upgrade as money permits, but this won't be right away. Obviously, I wouldn't be able to afford the best USB interface.

So in this context, what is the best way (in terms of sound quality) to get sound from the computer? Would it be better to get one of those integrated USB/DACs with built-in cable? If so, I'm guessing this would mean money down the drain when it comes time to upgrade.

Also, many mention that using coax or toslink from motherboard is not a good idea, but I don't see a justification for this other than USB is the way to go. Why is it that coax/toslink from the motherboard is inferior? On my computer at work I at least don't get constant ticks and pauses like I do when using the cheap USB->coax adapter I got several years ago.

The "U" in USB stands for Universal. IEEE 1394 (Firewire) is NOT universal. Most motherboards have dropped support for it. And so are most DAC vendors, sadly, have too. Universality often wins out over quality.

Motherboard based Toslink & RCA SPDIF signal paths are cheaply made, and sound that way... to me, at least. Even with the addition of a galvanic isolation transformer. I have listened to a dozen or more of them feeding a WEISS DAC 202, among others. (This was my job for a period of time) Consider that the entire motherboard costs $100, and they have to include a lot of other parts for those 100 dollars.

I'm not sure how to best invest $200. What inputs do you have on your "old D/A converter"? For less than your budget, a USB based M2Tech HiFace2 will get you RCA or BNC SPDIF out with quality clocks and galvanic isolation.

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USB is pretty pathetic. Firewire does blow it away. For $200 - heck - $150 - just get an ESI Juli@ soundcard. it blows away the usb at a much lower cost.

USB sucks - plain and simple. Use it to connect your mouse and printer, not a dac...