No problem using a portable hard drive as a media source
Laptop soundcards do tend to be noisy and a USB soundcard would help (would be preferable to have a quickish laptop though). If you're going the external box route, then perhaps a USB DAC would be the way to go?
How old is your laptop? The only problem in running a USB soundcard/DAC and hard drive would be the strain on resources if it was of a relatively old spec. If you've got an old crusty laptop, you would want to make sure it had USB 2.0 support. Very doubtful this'd be a problem if you've got a newish laptop.
Threre are quite a few 500GB external hard drives that can be purchased for around £70. Have a look at eByer. Avoid models with a fan. The noise is intrusive.
If you have a wireless modem/router, also consider a NAS type of HD. With a notebook, NAS will allow you wireless access anywhere in your house.
I use a Sound Blaster Audigy 2NX external sound card.
Discountiued in Europe but can be picked up at eBay at bargain prices.
It has analogue outputs but I use a well modded DAC.
I tried many rippers including EAC, then settled on CDex after incorporating 'cdparanoia' into it. Sound quality when streaming is better than the original CD!
Some new amps such as the Pioneer A-A9-Jhave USB connectivity.Has anyone tried them?