Airpot Express - Upgrade amp or DAC?

This is not accurate. DAC will improve AE since it has relatively low jitter on digital output but horrible jitter artifacts on analog out. You can find measurements here:

http://www.stereophile.com/digitalprocessors/505apple

Any jitter suppression, either by reclocker or upsampling (reclocking) DAC is always beneficial.

It sounds like you have done some critical comparisons already and have idenified a system weakness that you know can be improved. I would follow that lead and get a DAC that you know something about or have heard. The audition is always the single best advice you can get.

Kijanki - have you ever actually listened to an AE through a DAC??

I have made measurements and critically listened to many digital sources, including AE, Transit, Tascam devices, Apple TV, Squeezebox 2, 3, Duet and Touch, Sonos, Lynx cards, RME cards and others.

The standout worst of these is the AE and Sonos. No DAC will reclock these enough to make it musical except maybe the PWD in NativeX mode. Silly to drive such a DAC with an AE...

The jitter reduction capablilities of 99% of DACs is dissappointing IME. You are better off to reclock the source if you intend to use a high-jitter source. This is cheaper than buying a really expensive DAC and works actually better.

If you read the last 10 reviews of DACs in TAS and Stereophile, you will find that they often use an Off-Ramp to drive them to determine the performance with a low-jitter source. TAS concluded that even $1K DACs can sound as good as $8K DACs if a low-jitter source is used.

Steve N.
Empirical Audio

Yes, I use Benchmark DAC1 with AE and sound is incredibly clean up to point of being too clean. You might not like sound of the Benchmark DAC1 or any upsampling/oversampling DACs but cannot deny its jitter suppressing ability. Measurements taken by few reviewers, including Stereophile, confirm it. In fact all the measurements of Benchmark DAC1 are phenomenal.

http://www.posthorn.com/Bench_5.html

"You might not like sound of the Benchmark DAC1 or any upsampling/oversampling DACs but cannot deny its jitter suppressing ability."

It is an okay DAC at this price-point. I modded the DAC1 for almost 10 years, but I dont mod anymore. I have a lot more experience with DAC-1 than you do. I completely redesigned it in my mod including replacing the clock with a Superclock, op-amp swaps, eliminating several op-amp stages and lots of power supply changes. I even put I2S interfaces on many of them. There are probably 100 of my modded DAC-1s out there still in use.

I can give some anecdotal evidence for the stock unit:

Both my testing and reviews I have read demonstrate that each of the digital inputs sound different and changing cables or sources makes a difference. I am not saying that jitter is not reduced, because it is, but because it is a resampling DAC, you hear the jitter of the clock in there. The PLL is also affected by jitter, so jitter on the incoming signal does matter, the lower the better. This is the common thread with most DACs and this one is no different. There are only a couple of DACs that are truly jitter-immune and they sound like the internal clocks, which is not always a good thing.

IF you buy stuff based only on measurements, I am sorry for you.

Steve N.
Empirical Audio