Because I use a laptop for live performance this was something I have played with over the years. Believe it or not, Some laptops boring old mini jacks are totally up to the task of playback of audio files. I use Win Amp. I tested a few laptops, If you install an audio editor like wave lab, and put it into record with nothing plugged in and the mike muted, you'll soon see what the noise floor is.
My first laptop an Acer had a terrible hum and noise floor so I tried using an audio interface and the stupid thing would crash on me.
I had borrowed a friends Mac Book and it was dead quiet? I then borrowed everybody in the families laptops and found it was hit and miss.
The quietest was my sisters Asus. So on a chance I bought a Asus netbook. It works. No Hum, no noise floor. I play it LOUD through a PA. Mini jack and a realtech sound card. So
before you spend money on something that will be a PITA to drag around, see if you can score a netbook or Tablet that just happens to be OK at audio.
Those Express card options are also a good idea, but I found them expensive for what you got.