As far as loading goes, I have found that with my current phono pre (ARC PH5) I settled on 200 Ohms for my Benz M2. With this pre you can toggle the loading using a remote, its very easy. But I will say that the dif between 200 and 500 was pretty small.
I have the LS-100 in for evaluation and will be trying the phono stage as soon as my 12AX7 comes in. I took a look at the resistor arrangement in the phono section and there are two pairs of 100 Ohm and 1k resistors in addition to the 47k. This gives you settings of 50 (2 100s in parallel), 100, 500 (2 1ks in parallel) and 1k. What would be good for both of us would be to replace the 1ks with 500 Ohms. Then you'd get settings of 50, 100, 250, & 500. You have to pull the phono board and replace the resistors. Space is pretty tight, so I don't think you could parallel up each 1k, which would do the same thing.
EDIT: After a little more thought, it would be easier to replace one of the 100s with a 200. Then you would have settings of: 67, 100, 200, 500, & 1k.