I do not know if an AC power adapter, such as the PX-2G can be reliably diasy chained, even if there is plenty of power to run the two devices.  In any case, daisy chaining ANY Line 6 pedals is definitely not supported, and if you ran into trouble, Line 6 could deny warranty service.  Folks that have daisy chained pedals, such as the ToneCore pedals frequently report adverse sound performance anyway.  Line 6 pedals are VERY demanding when it comes to consistant power supply.

Consider also that the Line 6 folks do have to tow the company support line, not to sell additional product )I don't think they make a ton from selling $20 power supplies), but to avoid warranty disputes.

What you might want to consider is a good quality, regulated power supply that can handle multiple stomp boxes, including the Line 6 4-button stomp boxes.  Take a look at this Line 6 document.  It suggests several VooDoo Labs power supplies as a possible alternative to the PX-2G's for running Line 6 4-button stomp boxes.

http://line6.com/support/docs/DOC-3965

I would recommend the Pedal Power 2+, which can power both your MM4 and DL4, along with a bunch of other devices.  You might also consider Pedal Power AC, or Pedal Power Digital, depending on your needs.

http://www.voodoolab.com

Also, here is an interesting Line 6 Forum post from about a year ago that also addresses the topic.

http://line6.com/support/thread/55666

Safe travels,

Charlie