USB to Coaxial

I assume you mean the input of the DAC is coaxial?

USB to USB there is a chance of some electrical noise.

USB to coaxial should eliminate this, as coaxial cables don't use electricity.

Chances are you won't hear the difference either way, but coaxial is a safer bet.

I've never used one personally so I don't have any recommendations, but apparently they are quite expensive. Around $200 seems normal. So if you can find a DAC with a USB option that might actually be more affordable. This is the cheapest one I could find through a small amount of Google searching: http://www.musicdirect.com/p-60917-m2tech-hiface-usb-to-spdif-interface.aspx (edited, new link)

Seems to be much more complicated than other adapters.

EDIT: Actually there are some cheap ones hiding behind the pricey ones...

Quote:

Originally Posted by Theoman 

So am I better off using USB or optical with adapter?

So your iMac comes with USB and optical output?

Why not just sell off your current DAC and get a DAC with optical input? (or optical & USB input).

What is your current DAC?

Quote:

Originally Posted by Theoman 

Is USB to iMac better than optical to 1/8 adapter?
 

Is this your question?

So using USB from iMac to USB input on DAC?

or iMac optical (1/8 port) to optical input on DAC?

I'm far from an expert on this, but my gut says optical.

Just get an external DAC with both a USB and optical input. see what sounds better to you.

I'm assuming you planning on plugging your headphones into the DAC?

Quote:

Originally Posted by Theoman 

Here's what I'm trying to connect. Burson 160 headphone amp, PS Audio Digital Link III and Imac. What I'm confused about is do I use the USB or get a optical adapter? what is better for sound?

You have a DAC (PS Audio Digital Link III) and a headphone amplifier (Burson HA-160).

I'm assuming you already have the RCA cables to connect the PS Audio to the Burson HA-160.

So all you need is one USB cable and an optical (1/8 to Toslink) cable.

You hook up both cables between the iMac and the PS Audio and test the sound using the USB connection and test using the optical connect and see what you like better.

Unless I'm missing something?

I would just USB for now(unless you already have an optical cable). If you pick up any electrical interference, which is relatively unlikely,  consider switching to optical. 

As far as actual sound quality goes it doesn't matter. 

If you computer has optical out, which new imacs do, don't bother with a converter as that would be completely pointless.

Aloha Theoman, Check out Mtech2 Hiface usb to s/pdif coaxial.  This may work for you for now...

Quote:

Originally Posted by Theoman 

Here's what I'm trying to connect. Burson 160 headphone amp, PS Audio Digital Link III and Imac. What I'm confused about is do I use the USB or get a optical adapter? what is better for sound?

So you've got all the toys you need. If your ears can't be trusted to determine which connection sounds better, here's the theory.

1. In order to be decoded properly, the digital data which represents audio signal must be fed to the DAC in specific time intervals. The accuracy of timing these intervals has some impact on the perception of sound quality: the more accurate the clock that controls the rythm, the better it sounds.

2. There is a difference in the way digital audio is transmitted through USB and S/PDIF (which covers optical and coax): USB passes the raw data to the receiver and timing happens on the receiver side. S/PDIF sends the data packages already timed on the sender side.

3. Computers are hardly ever bought for the quality of their sound circuits - it's enough to provide basic support and tick the box at the lowest possible cost, as 99% of the buyers don't care about the high-end audio. Consequently the clocks used in basic audio circuits have reputation of being pretty inaccurate.

4. Dedicated DACs are usually bought to squeeze the last drop of performance out of the audio system - consequently the components used there are typically much higher quality.

By now it should be obvious which connection would provide better quality: for your setup I'd go with USB and never look back. However if you have a high end CD player as a source, the coax connection may be as good or even better.