Wouldn't you be able to get the same effect by applying some digital filter to the music? Same goes for warmer sound some people claim for analog amplifiers. I would think you should be able to tune your digital devices to produce the same sound.
In theory you could compress and add some flutter. [1]
The problem is, you don't have access to the master - if you try to apply this filter on top of a final mix destined for CD/digital, it won't sound the same as tape, and will deteriorate the signal even more. That's why some bands still release on cassete, you actually need to mix w/ tape in mind.
