Need help choosing a DAC for my Macbook

Hi

I have a MacBook Air and would like a DAC. My thoughts are as follows:

Connections: I have an electronically noisy environment, so I am thinking that toslink out of my MacBook Air is best. This also frees up a USB port of which the MBA only has two. However, i believe that the jitter over toslink isn't great out of MacBooks in general so wouldn't mind USB if the difference due to jitter is noticeable.

I also have an unused thunderbolt port just sitting here. Thunderbolt supports audio and has very good data transfer performance so I figured this could be a potential option. Some thunderbolt DAC's might come out next year but they'll be too expensive for what they offer. Is there such thing as thunderbolt to toslink?

DAC: Due to the noisy environment, I think balanced outs would be greatly beneficial. I am ultimately running to XLR studio monitors. 

I like the idea of the Bifrost but it only has single ended (unbalanced) RCA output. If I went the toslink route it would save me a bit instead of upgrading to USB. The Halide DAC HD seems great due to its simplicity but again unbalanced. There's also the Apogee Duet 2 which is made for Mac but I don't need inputs and for $600 i think I could find better quality elsewhere.

Sidenote: I will be changing my MacBook Air out for a MacBook Pro soon, this shouldn't make too much of a difference right?

Any thoughts you might have would be greatly appreciated.

Thanks