Aww, yeah, loadin' up PSP.  I'm going to go over a bunch of SCSI setups, both legal and illegal, just to give you a feel of what you can and cannot do.  I'm probably not going to do anything with dual-channel adapters, because I'm not terribly familiar with them.  Basically, it's similar to having 2 adapters on one card.  

This is a no-no.  "But both ends of the bus are terminated, right?"  No they aren't.  Termination has to happen within 4 inches of each end of the bus.  See, termination really doesn't cut off the bus, it ends it.  Imagine a signal going down a wire on the bus.  It will go into a pin and also go past the pin to the end of the cable.   Here is a picture to better explain this: The "Device" is what the cable will be communicating with, and the Resistors make up the terminator.  It's not that simple, but I digress.  The resistors on the left really wouldn't stop the signals, while the ones on the right would.  But that's not how it works.  This is why you need to have the very last node on the cable terminated, and none other.

This one's obvious, the termination in the middle of the bus will mess everything up.

Many adapters today have 3 connectors of both (50/68 pin) types.  Unless this is a dual-channel card, one must not use all off the plugs at once.  The reason is, SCSI spec states that a stub (from the cable connector to the drive) must not be more than 4" long.  Unless you can mount your hard drive directly to your adapter card this won't work, as the setup would form the dreaded "Y" configuration (it's not a good thing).  The extra plug is provided solely for flexibility.

This setup is OK.  Even though it includes internal and external devices both ends of the bus are terminated.

Here's an example dealing with putting Narrow devices on a Wide bus.  The "T:x" is each termination.  I specified the adapter's special automatic termination settings, and I put a Narrow device on the Wide bus.  This forced me to use one of those special converters that terminate the High byte for you.  In real life, a sensible person would simply swap the locations of the two devices on the Wide cable, and avoid a costly converter.