New DAC recommendation $1K, hopefully tube.

MHDT Labs Havana was absolutley STELLAR!! I tried 8 DAC's in the last year, and this may have been my favorite actually. It is very musical, whatever that means, it sounds rich and full. It's just not as extended as some of the SS DAC's so I finally settled, happily, on the Bryston BDA-1. But I absolutely loved the Havana. I think anyone who has had one has loved it.

Although not a tube DAC, I would check into the New Wyred DAC. Great sound, great build and great price.
Wyred has an audition program.

Macdadtexas, those are the exact two dacs I'm considering at the moment!

I may upgrade the ap express to a mac mini so I'm also looking into a wavelength brick or another nos dac.

Never heard of wyred but will check it out.

The Havana is a great DAC (I own it), but I don't think it's well known for jitter reduction. I use mine in a second system (under construction), and will go USB with it from a Macbook I3. In my main system, I use a Mac Mini, and I insert an Empirical Audio Pacecar to reclock and address the jitter issue to my DAC. That said, I've also run optical cable directly from the Mini to my DAC (a Modwright modified Transporter), and it still sounds really good without the Pacecar. I'm not sure how much the Transporter DAC is jitter immune (I think they do present it as somewhat jitter reducing) compared to the Havana. But for some reason, gathered from previous readings, I think that there would be less jitter using a Mac Mini and optical than using the airport. And what really matters is how the end product sounds to you.

Without getting too technical, the airport express does exhibit a fair amount of jitter, and the Havana's strong-point isn't jitter reduction; it also doesn't have balanced outputs and it's digital input selection is limited. That being said, I have one (in addition to a Bel Canto DAC3) and love it. I'm running it from a Mac Mini and use the Bel Canto USB link (although there are many usb to spdif converters) to go from usb to spdif in the Havana. In general, i don't think airport express is the way to go for a server setup, unless it's for more casual listening. If you can find a used havana and get a good usb to spdif converter, it will keep it around 1000. The biggest difference, no matter what DAC you get, could be getting away from the airport express.