A soundcard of some sort. I'm using toneport ux 2 from line 6. I had an idea that might work. You know, people here seem to agree on that the direct out sucks ass tonevise and micing is the way to go. So what I came up with is using the slave out on the amp and into the toneport turn off amp sims but leave the cab sims on. That way the signal coming from the amp is both from power and preamp. The direct out is just the preamp with some added circuitry to simulate speaker load.
Hope this helps
Geiri