Integrated $500-1K for Classic Jazz

I have been reading through posts on this forum, which has been very helpful, but I am hoping to get more specific guidance. My current system is as follows: (1) NAD 320BEE integrated amp; (2) Wharfedale Pacific Evo 8 bookshelf speakers; and (3) Arcam CD72 cd-player. I use audio-art cabling and run everything through a ps audio duet power cleaner.

This has been a budget system in the making over the last 5 years. I listen exclusively to classic jazz - piano, trumpet, trios, and jazz vocals. The one thing I've always loved about the Wharfedale's is their exceptional midrange -- very clear, warm, and superb for vocals. The Arcam was the newest addition, and is wonderful. I'm looking to upgrade the NAD integrated. It's served me well, but the one thing I think I've really noticed is that the soundstage and imaging is rather poor. You don't get that sense on well recorded albums that there is separation between the instruments; the clarity and focus of the sound is lacking. Perhaps I'm simply looking for a slightly more forward sound? I know that the Wharfedales and NAD components are generally considered "warm."

I've been somewhat spoiled because I was able to "borrow" my father's musical fidelity amp and preamp for the past few months, and the sound is breathtaking. What I'm hoping to do is improve my integrated amp for under $1000. I'm open to good used gear. I know my budget is rather small, but anyone have any ideas?