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
After doing some searching, I'm going with your advise.  A silver starlight 7 USB.  Arrives tomorrow.  Very interested to see the affects it may have :)    I couldn't afford the platinum but i got the Silver used for about the same price as a new entry level cable. 
Friend
You should have a complete System after your Wireworld arrives!  With a
MacBook Pro and its already stellar design feeding the excellent Wireworld which will feed the McIntosh MHA100 - you should be in the house for quite awhile enjoying Music. 


Best upgrade for streaming? Ditch the laptop as a streamer. It's not made for that.

There are plenty of purpose built streamers out there, even much cheaper than a laptop. They also free your laptop for other usage, and look better. Some examples in budget: microRendu, SOtM sMS-200. Bluesound Node 2, and Cambridge CXn
I didn't realize that.   Do you get a an appreciable gain in performance from a range of $500 Streamer to $2000 streamer?  And i'm not necessarily in necessity of storage capacity 1T/ 2T, etc..  I'm more keen on sound as determining factor of value for purchase.