I also have a WGS 6150, not that it's anything special (or different from stock 6100). For some reason it provides a 'warm and fuzzy feeling' simply from having that badge on the front. Just about everything I own Mac-wise has come from the US through eBay. Persistent searching was key, although certainly the supply of computers and parts of this vintage was much better many years ago when I acquired the bulk of it.
One oddity I have, since we're talking about 9150's, is a Q950 in a 9150 shell. The difference between the two cases is the original Q950s had silver-colored electroplating for shielding, while the 9150 had gold color and the cut-away for the floppy drive moved down to make way for the DDS tape drive. As I understand it, Avid wasn't ready to move away from supporting and supplying the Q950-based Media Composer systems, so using their 'leverage' they managed to push Apple to manufacture and ship more Q950s much later on. These ended up being installed in the gold-lined 9150 shells that were part of the active production of the day, just with a normal Q950 front bezel with the floppy drive in the top. To make things even more interesting, these systems came stock with a PDS PowerPC upgrade card, which I believe had been standardized to 100MHz in Avid's config. Media Composer will only run in motherboards they officially allowed, so the possible base configs were limited. I over-clocked the 8100/110 board in my Avid AMP chassis to 40MHz bus, after which the software refused to recognize the computer as a supported model.
The silliness of the 9150 reversed slot order began with the Q950 being backwards from everything else for no reason I'm aware of. It survived in the 9150 because the PowerPC motherboards were offered as drop-in upgrades for existing Q950 systems. Preserving the odd slot order was the only way to ensure this transition went smoothly with the established card order in the Q950 systems already in use. It was actually a major pain when I was expanding my Sonic Solutions system because all the boards are linked internally with custom a SCSI cable that only fits properly in one direction. Creativity was required to get this solved. Eventually I managed to locate a Sonic Solutions nubus expansion chassis, an extraordinary rarity, and proprietary, which freed the cards from the confines of the 9150 case.
I'm aware of the limitations of no video cards in the Digi expander. That said, just about every variant of expansion chassis I've ever tried caused the host system to puke if video was in the expander. Just about the most useless, non-functional case was that of the Second Wave expanders, both the nubus 4-slot and 8-slot, and the PCI-to-Nubus version. Just about any cards that would have been useful or high-performance were a no-go. Perhaps they would have been more at home in an industrial data-acquisition setup. I sold off all of it to collectors. Someone lucky-enough to have owned the SE/30 host card for the 4-slot model might have had better luck with creating a working configuration. My preference for dual video would be one PDS plus one nubus, because two high-performance nubus video cards together is asking for trouble even if they are identical. (I did manage to get two 1600x1200 PCI cards stable in my 9500, however, and on custom-made mode/wiring adapters to 13W3 cables for SGI monitors at that!)
As to music, while I appreciate quality in just about any form of tunes, my listening passion is electronic music. From simple ambient or creative random noise all the way through to the hardest and fastest of beats, I marvel at how a 99-percent-plus synthetic instrument and sample pallet can appeal on such a wide scale to a basic human tribal instinct. As much as some people don't 'get it', to many others it can induce the heights of emotion. Sometimes I just like to listen closely to the types of individual sounds that have been created in published music and wonder what chain of processing could make them. Often a common effect can result in unrecognizable change in a sound if the parameters of the controller are taken far outside the normal bounds. I also greatly appreciate artists who manage to incorporate all of this with ordinary band instruments successfully, of which Radiohead is probably one of the most well-known examples. I actually enjoy their creativity and quality more than the actual music itself!
While I am no expert in music production, I have a strong desire to experiment with creating unique sounds that I can build into arrangements. One of my family members is much better at musical composition than I am, so I may lean on his strengths to take what I create and assemble them into musical forms I wouldn't be able to visualize myself. A real bonus of working with electronic sounds and having an open creative direction is that often the 'crudeness' of older equipment actually works in your favor. The popularity of "chip-tunes" right now is a fine example. Another would be specific synth flavors from well-known ancient computer and video game consoles being resurrected in established modern music forms. Even the crudest of early 'drum-like' synth sounds from the Casio VL-Tone VL-1 micro-keyboard that was never intended for serious music-making have ended up in some recent hip hop tracks due to a somewhat cult-like status for the device. (I happen to own one of these.)