Hi Folks,
a difficult question, Rikki, because the books were written for their intended machines. Again the "How Do I" 6500/6000 book exercises will probably not produce the intended musical results because the presets will have changed. The principles of the exercises however will still be valid. Some chapters will not apply, no custom section, custom panel, home page or favorites programming, harmoniser or style converter, I would imagine without looking closely. The rest is pretty much applicable in principle.
The "Getting The Most" 7000 book section 1 is pretty universally applicable to everything. Both 2400 and 2600 have usb so the Song Manager and Audio Recorder apply. The 2600 is supplied with Jukebox and card reader here so Jukebox and digital audio and the SD sections also apply. However tabs and slideshow will not. Apart from custom, many SD functions are identical to floppy, so the principles of save, load and file management are the same.
Potential purchasers need to bear all this in mind before buying