The collection of SCSI devices attached to a card are referred to as its SCSI chain. This chain needs to have its ends deliniated by electrical circuits referred to as termination. Termination comes in two types: a simpler passive version that is essentially a resistor, and a more robust active version that uses more complicated circuitry. If you've only got one of the possible types of SCSI devices connected (say, just some external devices), then the last item on that one part of the chain needs to be terminated (last meaning the one farthest away from the controller card), and the SCSI card itself gets configured so that it terminates the other end. If you've got two of the types, say both internal and external devices, you need the last device on each end to be terminated. You can't get all three going at once with any SCSI card I know of; you can get regular+wide going, or regular+external, or wide+external, but not all three. For most people, wide SCSI drives are more of an annoyance then helpful anyway; if you've only got one drive, it's really not worth bothering with the minor performance improvement you get from wide drives over regular SCSI drives. Essentially, if you don't really don't know why you might need a wide SCSI drive, then you really aren't in a position to need them; don't sweat it.
Hanging off my PCI Adaptec 2940W SCSI controller, I've got wide drives and some regular SCSI devices as well. Because of that, I can't connect external devices, so my best option was to get an internal CD-R drive, which is what I did. Connected to my SCSI card are two wide drives, a regular CD-ROM drive, a tape drive, and now the CD-R drive; five devices total. Hooking up that many devices, all running at high speeds, becomes an incredible pain. Cables and termination that worked fine with a smaller number of devices can suddenly stop working when you add one more to the chain. Total cable length and connector spacing become an issue. There are a couple of recommendations here for when you start running into problems with too many devices (typical symptoms include erratic data errors, SCSI bus resets, and things just plain old not working). First, use active termination if at all possible. Often, you'll only have a small number of devices that have active termination; move them around so they're at the end of the chain, with the passive-only devices unterminated in the middle. Second, make sure you use the best quality cabling you can afford. If you've having consistant problems, the best source for SCSI cables is Granite Digital, a company that doesn't sell much else. They supply superior external cables, and can build you custom internal ones; prices are a bit higher then average, but so is the quality of what you're getting. My system used to work just fine when I had only 3 or 4 devices, but adding a fifth one brought a variety of odd, intermittent problems out from hiding. In order to get everything working properly, I bought one of Granite Digital's wide active terminators and used it in the place of the active termination that was available with my hard drive on the wide end of the chain. The internal Yamaha CDR-100 has active termination available, so that's terminating the other end. There also is some fancy footwork to do in order to get the Adaptec 2940W to accept all this as well; check the manual for how the termination settings on your SCSI card need to be configured for the types of devices you have attached. In order to plug everything in, I also needed to buy an adapter from Granite to plug into my existing cable; if you're buying one of their active terminators, you'll probably have to buy a SCSI cable from them to hook it into yourself, which is a good idea anyway. After going through all this trouble, I average one SCSI error every 8GB or so of data I feed through my tape drive, which I find acceptable for my personal system; as long as the tape drive isn't involved, I never get any other errors. CD recording always goes without a hitch, which is the important part; I can deal with a tape being flaky sometimes on a personal system.
Some information about SCSI controllers is in order at this point. There are a couple of performance distinctions between different models regardless of manufacturer. Bus-mastering controllers can perform their I/O without hogging all of the CPU's power to do so; this is almost an essential capability for serious CD-R work. Most of the cheap cards bundled with drives aren't bus-mastering, and they run out of steam when you start pushing them because of it. The other big distinction between cards is what bus type they use. The newer PCI cards (and, to a lesser extent, EISA and VLB ones) can throw data around much faster then the older ISA style ones. If reliable CD-R is important to you, you really should be getting a bus-mastering PCI SCSI card. Whether it supports wide drives or not is usually not a real distinction for most buyers, but the price differential is usually small enough that it's worth spending the extra money to get the wide support. The only controllers I recommend are either from Adaptec or DPT. Adaptec's 2940 series is what most people seem to be using for CD-R, and it's a good choice (their 1542 is also good if all you're going to be running from the card is the CD-R). Downsides include the fact that every time Adaptec releases a new version of their card, everyone needs to update all their software drivers to use it; as long as you're sticking with mainstream OSes like the Windows variations, this is not an issue for you. DPT's controllers can be faster at the same price and are more expandable in the future; they are also better about keeping their drivers working with newer cards. The downsides are that lower sales mean you won't find as many people who are familiar with them, and software support for all the latest things that come out tend to lag behind Adaptec's releases. I didn't buy a DPT controller for this system because the only ones they had available at the time were too long to fit in any of the PCI slots on my motherboard; it would be a close call if I were buying a new one today, but I really can't recommend DPT for the casual SCSI buyer. Everyone else making SCSI cards, I can't stand, so I won't talk about them.