I want to use both the internal and external SCSI devices with my A2091.  To my surprise, I see that the terminators on the card are not socketed and it doesn't appear that there is a jumper setting to disable termination. (Really?!?)  

Before I physically cut out the resistors and pick up a DB25 terminator, I just wanted to make sure that I'm not missing some less drastic way of removing the termination.

The A2091 SCSI controller needs the termination on it no matter how many hard drives you install. The place for the end termination is the last on the cable chain. Both ends of the SCSI cable need to be terminated and the A2091 is at one end of the cable.
http://www.sacc.org/2091-man.pdf
has a user manual. I have not used one but what I have read they need a revision 6 rom ( prefer rev 7) to work with an OS2 or greater.

Both ends of the SCSI cable need to be terminated and the A2091 is at one end of the cable.
http://www.sacc.org/2091-man.pdf

No, it's in the middle when you have both internal and external drives connected to it (see below). It becomes one of the seven devices in the complete external/internal chain, and physically, it is exactly in the middle of the  chain.  The A2091 manual you link to above states:

"If multiple SCSI hard disks are connected to the A2091, you will need to remove the terminator packs on all but the last external SCSI device in the chain, and all but the last internal SCSI device in the chain"

Ditto. Both ends of the SCSI chain need to be terminated. If you rip the internal ones out you're likely to "terminate" your 2091.

I don't think this is true. I ran an A2091 without the onboard terminator for years without a problem. I also read about others doing this before I did it.

The thing about the A2091 is that the card becomes the centre of the SCSI chain when you have both internal and external devices.

External devices <----into----> A2091 <---into----> Internal devices.

If the card has termination, then you've placed a terminator smack-dab in the centre of the chain. The resistor pack on the A2091 is right beside the SCSI 50 pin connector.  If it's terminated it means you have termination at the middle of the SCSI chain, which is not correct.

So, remove the internal terminator, and as long as you terminate the last external device and the last internal device it will mean both ends of the chain are terminated.  If you ever need to terminate the A2091 again you can either install a socket for new resistor packs, or buy an in-line 50-pin pass-through terminator to place in the on-board socket.

This page among others recommends removing the resistor packs when using both internal and external devices.
http://www.wonkity.com/~wblock/SCSI/SCSIExamples.html

However, before going to the trouble of removing the on-board terminator, I recommend the original poster just try it with them installed.  Sometimes SCSI works in mysterious ways.

It would seem so:
"The most common mistake in SCSI termination is assuming that the SCSI controller itself doesn't count; in fact, it does count as a device, and the termination rules apply to it just like other devices. Many Amiga controllers have the termination resistors soldered into place, under the assumption that only internal or only external SCSI devices will be attached. If both internal and external devices are to be used, it is necessary to remove these resistors. Soldered-in terminators can be desoldered or simply cut out. Sockets may be soldered in their place to provide the greatest versatility, or you can just use external terminators. "

As mentioned above I have used 2091 before for both internal and external devices and it has worked flawlessly. I have never had to remove the internal termination.  My coments were more about the dangers of unsoldering compents from old hardware and premature termination.