Steelers,
I've only hunted the Imnaha once, but I'm willing to share. We parked at the Tenderfoot trailhead and hunted in from there. I would also try the Indian Crossing trailhead and the McCully trailhead.
I don't know that you get away from the crowds, but that is mostly perspective. We saw more elk and fewer hunters than we were used to in W.WA, so we were happy. The farther we hiked in, the more horse camps we encountered. So, if on foot, you may want to find that happy medium between the day-hunter's range and the horse camp that is packed in 10 miles. That is a narrow bandwidth.
I'm either headed back there or over to the Snake River unit again this year. I've ridden horses in the Snake River unit, but not hunted there. The outfitters and hunters I've talked to all say about the same thing: you can't escape other hunters, but the harder it is to get to, the lonelier you'll find it. Not a lot of news in that advice.
Shawn