in post # 13 there are some pictures as to what this cabinet looks like http://www.avsforum.com/avs-vb/showthread.php?t=1173635
This is exactly what I am having built here localy. The open back in the first picture shows what it is I am dealing with. Stiff cables will be a problem. Drilling holes in the back panel is not what I prefer to do.

Blue Jeans has this on their site. It is more flexible than others and will work fine for your application. If you really need extra flexibility, I suggest getting the cables long enough so you can let them rest on the floor for support and then they can avoid real sharp bends and twists. Just remember to keep some distance between them and power cords for best performance. You could also try removing the back panel altogether. Cutting more/bigger holes is what I would try first.

Belden 1505F:
Belden 1505F was our recommended audio cable prior to the introduction of LC-1. It also has double-braid shielding, and is a bit thinner, more flexible, and more economical. If you will be wanting to have your audio cables bundled together in Techflex wrap (see below), we recommend 1505F because LC-1 becomes quite thick and heavy when bundled and can pull hard on equipment jacks. View the technical specs for Belden 1505F.

I looked at you pictures (that is a very nice credenza). It looks like from the picture where the back of the credenza is shown, that you need to route the cables through the large predrilled and finished holes either down or across the back into another bay. Is that correct? If so, I believe the Monoprice premium RG-6 based cables would easy be flexible enough. They are certainly cheap enough that you shouldn't really be hurt by ordering one and testing it.

It is correct.

I should have posted that if you buy a single monoprice cable, you can also determine if these cables are of sufficient quality to meet your needs. Besides Blue Jeans and Monoprice, Outlaw has its own line of interconnects plus resells part of the Perfect Path line.

Wow. That looks like a challenging run.

What about using some Right Angle Adapters for the connects close to the hole? Some combination of right angle and straight cables might get you what you need.

Looks to me like you are going to run out of room real quick.

I was thinking about right angle adapters, too, but those create a whole separate problem with wiring (namely conflicts with adjacent connections).

This may be the engineer in me pushing against aesthetics, but I am a big proponent of having decent access to the back of my gear. It makes ventilation better, it reduces headaches during setup, it leads to fewer mis-connections and loose connections, and it tends to make for tidier wiring.

How will you access the units to make the connections? Will they have to slide out (meaning you need 18" of slack to allow the equipment to come forward while remaining connected), or do you have a way of connecting the gear once it's on the shelf?

My 990 and 886 are too deep for my cabinet so I built a shelf extension on the back of the cabinet and cut the back panel out to allow the whole back of the 990 to stick out back. It made for great ventilation but it also makes it a lot easier to access. I use right angle connectors for my sub inputs and can tell you they won't work on the back of your gear because they take up so much space and they are not deep enough to let your cables attach without a lot of stress on the jacks.

My equipment will slide in from the back asthere is a removable panel.
I could be happy hving all my gear sitting on cinder block with wood planks. It is my wife of 37 years that has a problem with it. I am no closer to winning this battle than I was 37 years ago. Aesthetics is everything to her, and seeng wires is a phobia she has yet to overcome.
Some of my " cheap " rca cables will work fine but are over 30 years old, so failures with them could be more problematic as time goes on. I plan on replacing all of them .
The flexibility I am looking for that, I can make work, is that of Radio Shack Sub cable
The sub cable has no markings.

I'd suggest ordering a couple sample cables from MonoPrice and Blue Jeans (the Belkin 1505F that is available for analog audio as well as digital audio & video), testing them, and then ordering a batch of new cables once you find ones that have the combination of flexibility and sufficiently short plugs that you need.