I am by no means a DJX expert, but I will attempt to answer most of your questions:

1) Is the sampler section a one-shot?

The sampler is one shot. It can be set to start via trigger (you edit the trigger threshold) or you can actually trigger it manually.

You can edit the end-point and the loop point.

2) Can the available sample be divided between several sounds?

The DJX offers a total of 6 seconds of memory. You ercover what you trim off when you edit the endpoint. You can assign the sample to a single key. Just like the sampled drum loops that come standard on the DJX.

3) What kind of frequency response does it have, compared to the usual, muffled "toy"?

I think there are some very useable sounds... DX7 type fm keyboards and a few others are useable. In reality, I can only use about 20 - 30% of the onboard sounds with my other gear.

4) Will it save even one sample onboard a la Flash Bank or must you reload it every time?

The sample will be stored as long as the internal memory backup battery is good, or you don't do a reset.

5) Can you directly transfer a trimmed sample from a larger unit such as an Akai into the DJX?

No.

6) Will it save/reload programs via SMF?
Yes - either by bulk load or with an external sequencer.

7)What kind of sys-ex compliment does it offer, if any?

Too many to discuss.