6100 PPC connect to a modern LCD monitor

The CRT displays and the display cards you mentioned support the traditional 4:3 Width:Height aspect ratio. There are LCD displays that continue to use that aspect ratio, and are connected with VGA connectors, but you will have to shop for them.

The newer LCD displays use the "letterbox" or "HiDef" 16:9 aspect ratio, and will not be well supported by the hardware you want to use. Not well supported is a problem because an LCD will display at its best only with the correct resolution -- it cannot do intermediate resolutions very well at all.

The specs for the stock 6100 are available here:

http://docs.info.apple.com/article.html?artnum=112290

It lists support for 7 inch Nubus card and a PDS card - Processor Direct Slot card.

It lists the available display resolutions, and the choices are rather weak.

The 6100 with the AV card is a bit more capable:

http://docs.info.apple.com/article.html?artnum=112291

I have a Performa 6400 that is hooked up to my "HD TV Monitor". Its only 15", but it worked great. I have an ever-so-common Mac-to-VGA adaptor hooked up to the mac, then just run a standard VGA cable from that to the "HD TV Monitor"

It runs fine and looks great!

You can hook an LCD up to the built-in video port on your 6100s without a new video card. The LCD will be able to run at least as well as your original displays. They may run even at a higher resolution, but that isn't guaranteed. You won't loose any capability with this change but you will need an adapter to use an LCD.

If you happen to be replacing Apple AudioVision 14 displays (how could you!!), you might not have any adapters to start with. But if you had any other display, you should have adapters that convert the rather large port on the back of your 6100s (called HDI-45) to a typical Mac monitor port. You can get an additional adapter that goes from the typical Mac monitor port to a VGA port, the port that your LCD will have. So it will go LCD -> VGA to standard Mac adapter -> Standard Mac to HDI-45 adapter -> 6100.

You also could get one adapter that goes directly from VGA to the HDI-45 port on the back of the 6100s, but I'd recommend the dual adapter method if you already have the first adapter. That's the way I always did it and it left me the option of using any kind of monitor, VGA, Mac, or AudioVision.

If you do choose to install a video card, this will allow you to get higher resolutions and more colors on your LCD, beyond where you were before. You must also get a right-angle adapter for this card because the 6100 requires the card to be installed sideways unlike the 7100 and 8100. This adapter is somewhat hard to find. A Sonnet Crescendo G3 upgrade card can serve as a right-angle adapter but those are kind of pricey.

Note that some video cards are NuBus and some are PDS. You need the proper right-angle adapter. The Sonnet Crescendo G3 upgrade card works with PDS video cards. (Most video cards for the 6100 are PDS.) Some right angle adapters are yet a third kind of strange slot intended to be used with a DOS card. These will not work with any video cards I am aware of.

Please check out this wonderful 6100 website, if not for reference, at least for fun:
http://www.kan.org/6100/

It explains graphics upgrades in fine detail.