Hi gbh,
I'm not a techy but understand that passive's are essentially just volume controls which in theory, add or subtract little to the signal path between source and power amp. As to whether they are any good, I think you need to judge this one for yourself.
I used a Creek passive pre amp (OBH22) for a number of years between a squeezebox touch and a Roksan power amp. I then replaced it last month with a Linn all in one streamer. The biggest criticism of passives is that they can sound a little sterile or clinical and I tend to agree somewhat with this suggestion.
You may, however, find a different combination of passive pre with power amp gives very different results - it's one of those 'suck it and see' answers I'm afraid.
Pedro