I honestly don’t think the amp will give you the imaging and sound stage, The speakers will do that. (I believe)
You have other threads about other amp questions so you seem to want a different amp for sure.
The Hegels for what they do are overpriced. Maybe they are superb, and bring out sounds and details you haven’t heard - with expensive cables and speakers, I would love to have one but they are definitely a step up from the NAD.
You can order a Hegel online for 30-60 day trials easily paying for a measly $20 shipping.
If you are to stick with your speakers, my feeling is that the raw power and hardware inside your NAD doesn’t work with your speakers well. It’s not the most musical sound. I would look for synergy, read a lot of reviews. Your budget affords you great choices.