Everyone's goal seems to be to use the IDE drive as a bootable drive, but could it perhaps be used as a simple storage media over the sound card, instead? Even if it was a DOS system, that had to boot DOS over MFM drivers or some such thing, couldn't you then proceed to load Windows, and every other program you want to store and load, faster since the soundcard drivers will have loaded by then?
By definition, the controllers for the drivers are on the drive itself, and the interface is simply a bridge between the system and the drive. However, it is 16-bit by design, and I don't know if I've ever seen an 8-bit soundcard with an IDE connector.
A possible plus is that ATAPI interfaces are more advanced than regular IDE interfaces so may be even more possible to run an IDE HDD over a soundcard than we think. I'm really getting antsy to try this, now. But then, I was working on computers before XT's were completely gone, and 386's and 486's were still very abundant, and I don't ever recall someone doing this.