With that in mind, I will again recommend getting an amp before a DAC.
Even after knowing that purplesaber had already ordered a DAC?
You read my mind! I saw a long thread about the Maverick DAC in other part of the forum and ordered one earlier today.
Purplesaber,
I still think you have made the right choice in getting a DAC, as the DAC in the AirPort Express is an obvious weak link. And for a $200 investment, is certainly the least expensive addition you can make right now, as you will most likely spend quite a bit more for either a preamplifier or amplifier.
However, Nuance's caution in using your volume control is good advice, as with too much volume you may be able to overdrive your present amplifier, and overdriving an amplifier and clipping the waveform will result in speaker damage more frequently than turning it up (within reason) on a more powerful amplifier.
I also think you should get acquainted with the change in sound at each component replacement and not be in a rush to replace everything at once.
It is true that a preamplifier functions as a switcher, volume control, and if so equipped, tone control and bass management. An active preamp, with an amplifying gain stage, can often give a fuller bodied sound to the music. Others prefer a passive "preamp" with no added circuitry or preamplification (provided their power amp has high enough gain, and many amplifiers don't).
I don't know if the Maverick D1 would be classified as a passive or active preamp, as I don't know if there is any internal gain (there is not much in the way of specifications or information available in that respect). You would obviously not have remote control volume when used with a power amp in place of your receiver.
I would agree with Nuance and others, that a power amp may be the next logical step. At that time, you can experiment with the difference between using the DAC direct to the power amp, versus through your receiver, as the receiver does have preamp outputs.
Steve