Never heard of 'Imperial malt'
Simpsons Amber if a dark toasted/biscuit malt. Think of the flavor of dark toast. Gives these flavors and aromas and a impression of maltyness. Over 5% it can be quite intense. Ive used it in fest beer and IPA for malty aromatics.
Brown is a must for brown ales. Again dark toast, but a bit milder and maltyier than Simpson Amber. I use 8.5% in my brown for a very brown ale.
Ive wondered about "golden naked oats' myself...