guidebook--Grant Amaral--Idaho the Whitewater State
It depends on if you are going to boat from the take out or if you have to drive back to the put in on where to go.
If you go back to the put in, the Lochsa (there are two awesome sections) and N.F. of the Clearwater are both awesome big water class III, IV runs that are a fun way to get used to the big water of Idaho. The S.F. of the Clearwater has two sections--both are pretty intense big and pushy and technical. The Mickey Mouse run would probably be the one to do, but don't put on too high.
If you go from the take out, someone suggested S.F. Salmon area--two problems--lots of driving (not good if you want to maximise boating days), most runs are multi-day, and the runs are pretty difficult. The Goat Creek section of the S.F. Salmon is a single day run, but it is intense pushy class IV, V in a wilderness setting. East Fork South Fork Salmon is like the North Fork of the Payette (class V) but in the Wilderness (intense!!)
So, I would suggest the Payettes instead--on the way from the take out to Boise. N.F. Payette, even the lower 5, is gonna be intense. I would say do the S.F. Payette. The Stairstep section is the easiest. Its big water class III with a IV here and there. Its super fun in a playboat and has awesome play. Also, the Canyon stretch has more class IV and can be done in a creek boat or playboat. Its really fun river running.
There are also multiple park and play spots up and down the main Salmon near Riggins and there are plenty of park play spots near Boise that are very active and popular. You can find out about those in The Playboater's Guide to Idaho.
I am a southeastern boater too. I have not found any low volume creeks in Idaho. I know there are some up in the panhandle and I know that Lolo Creek is a good class IV creek. I have put on some "low volume" stuff there and been scared out of my mind--its way different. Its always pushier than it looks and has lots of wood. I prefer to go run the big water class III, IV and try to prepare myself for runs in the future such as the NF Payette and East Fork South Fork Salmon--these are the class Vs there that people aspire to. My favorite runs are the Lochsa and the North Fork Clearwater. I usually am not much if a playboater, but Idaho is dreamy for playboating. The features are so big and soft and so different from anything around here. Its such a cool place to learn to get out in the middle and put your head down and charge into stuff. Its also good for your roll. River running on class III, IV there is going to feel intense compared to here, but there aren't many undercuts or sieves! Be careful of wood.
The water is cold and the air usually warm that time of year. The locals are extremely nice. Boise has an awesome boater scene with good beer hang outs.
Have fun out there!