One thing to consider before you spend your money is that you could just let the 6100 hang out until you find the HDI45 to DB15 adapter (or an audiovision) or until a better version of the whole machine comes along that you want to buy. Although it would be nice to be able to, you do not need to max out or even use or repair every machine you get. This is especially true if you don't have any vintage Mac networking infrastructure (localtalk, ethernet cards, whatever) or advanced data storage items yet.
If you have another Mac with SCSI, you could put the disk into that system in order to see what's on it. The SE/30 or 630 with an external enclosure (another thing that may be good to get, especially one of the ones that you can put 5.25-inch external devices into, such as a cdrom or 44/88 syquest or bernoulli drive into) would work.