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?
I have tried many solid state integrateds in your price range. My favorites were: Bryston B-60(still own), REGA Brio, and Arcam 65 watt model. All of these would work well in your system.
A used Musical Fidelity a3.5 integrated should work well for you. I had the a3.2 and a308 in the past and they sounded great with jazz. I listened to an a3.5 when they first came out and it was markedly better than the a3.2 to my ears. It would be a noticeable upgrade from your NAD and would be an amp to build future upgrades to your speakers and/ or source should you desire.
I see there are two for sale now on Audiogon. I have no connection to either seller.
I have not owned a Nad 320BEE but I have owned a B 60 and of all the integrateds,tuners and separates I have owned that sounded the best wih one exception. I have owned a Musical Fidelity 3.2 preamp which I used with a Bryston 4BSST as well as a Magnum Dynalab MD 208.The best unit I have had is the Nackamichi TA-3A. It is a Nelson Pass design which was modified by Stephen Sank. In its modified state it is the best sounding unit I have ever had. It has a huge sound stage, deep base, superb mid-range and a wonderfully clear (not harsh) upper range. I was tickled pink when I received it. Though it is not an integrated, but a receiver with an an above average tuner, the integrated part of it can compete with the very best ones I have heard. The best part of it is that I paid 495.00 USD. I have bought other things from him which have been equally superb and reasonable. He is, in my opinion one of the very best sound engineers around. If you are interested you may approach me for details.
You might also consider a Cayin A-50 that you can pick up for usually under $800. Great construction and great sound for little $$$'s
I second the Cayin suggestion, but look for a 70, little more power and some extra features. I had auditioned the 50 but felt the 70 had a little more 'push'.
Thank you all for the suggestions! I'll start looking into some of them - esp. the Cayin and Music fidelity. Here's a strange question though I suppose -- is it really worthwhile to spend less than $1000 on an integrated? In other words, should I stick with what I have for now and when I can move up to the next price level, go for that? Is the improvement over the NAD really going to be noticable for under a grand? I suppose this is a subjective question, I know.
Add to Mik971 suggestions, the Luxman 391 hybrid is quite sweet in the midrange (better than the 105 which is also decent). Jolida 1501 is also decent, particularly if you change out stock tube in preamp.
If you like the Musical Fidelity sound, I can also highly recommend the A300 which was the model above the A3. It delivers a very sweet 150 w/ch and can be had for under $1k 2nd hand. I previously had it driving $6k Mordaunt-Short Performance 6 speakers and it was in no way outclassed. It now resides in a 2nd system with Usher Be-718s. A super amp.
In answer to your question, yes, it is worth it to spend up to $1,000 to upgraded from the NAD 320bee. I had the NAD, along with the MF integrateds I mentioned earlier. The a3.5 or the a300 as Hens suggested would be a significant upgrade.
I've owned the NAD C320BEE (used it in my office system) and I thought it served the purpose quite well. Given your current system, I would spend the money on a subwoofer instead of electronics. And unless you're running out of power with the little NAD, I wouldn't expect significant improvement from an amp. You'll get much bigger bang for your buck with speakers than electronics.

Having said that, if you still want new electronics and you don't need remote volume control, I'd consider an ATI amp and an NHT passive volume control.
YBA 201 or Integre DT would be good choices, and my pick if I were limited to a $1000 budget.