Which is the best upgrade for the money for steaming from lap to through amp?


I am looking to upgrade my system with either a line conditioner or USB/Digital cable.  Am budgeted to spend about $500.

I am current running a mac pro to a McIntosh MHA-100 Amplifier and headphones out from amp.  

So where will I get the greatest benefit in transferring the sound quality to my Headphone?  Form the Line conditioner to the lap top and amp or from the upgraded cable from laptop to Amp?
128x128stephentp
Have you considered a USB to S/PDIF converter?

I use an old Macbook Pro, with Halide Bridge (USB to S/PDIF converter) to DAC.
All in one cabling is an advantage for me.
Also have an iFi USB Silencer.
At work have a M2Tech Hiface2, which was recommended to me.

I'm considering upgrading the Halide Bridge. It's limited to 24/96.
Although I have no 24/192 at present.
Also have

Have heard people talk very highly of Black Cat Silverstar Coax cable.
See if you can hear a difference if the Mac is on battery or not. If you do, you may need a replacement PS. If you can't, you are good. The real issue is ground loops and RF/EMI noise being caused by the PS.
Thanks for the input... that's something to consider as well which i hadn't considered. Best!