Have you been able to rectify this?
I have the same problem with a used VXP. This unit arrived without a bulb. The seller bought this VXP and two others new from PreSonusDirect. He is selling both others now on Ebay as well. He mentioned that one of the others arrived with the power switch NOT illuminating. I'd venture to say the bulb is missing from that VXP also.
From looking at the photo of the DigiMax, it appears the same power switch is being used on it that is installed in my VXPs (I have 2 now). The switch in the VXP is a DECA D16LAR1-1AB (available on Ebay from a seller in Taiwan only). He offers the switch with choice of 12 or 24 volt bulbs. The VXP uses the 48 volt bulb (due to it having the +48VDC Phantom supply for condenser mics). This seller has advised that he can order the 48 volt bulbs from DECA (China). If the DidiMax also has the phantom power supply, I's guess it too would need the 48 volt bulb. I have not been able to find this bulb (marked with D48V25MA) anywhere online. I have a request in to Bulbtown.com to locate this particular bulb. Their #6848 is the closest I can find but it has a different base than needed. Removing the red switch cap and the pushbutton is very simple (as is removing the actual bulb). I used a small pair of slip joint pliers to gently pull the cap and pushbotton out of the switch and a smaller pair of needle nosed pliers to pull out the bulb. No damage was done using this method. The switch specs are available (downloadable) on this Ebay seller's site (wonder_co). Simply search for DECA D16LAR1-1AB. He is apparently the only seller of the switch there. The switch (if it's the same) can be easily removed (partially or completely) from the front of product (after gaining access to the inside of the DigiMax). There is a round plastic nut holding it from inside. Unscrew the plastic nut and the switch comes out the front (you probably can unplug it to remove it completely if needed). The seller of my VXP actually purchased a new switch years ago for the other VXP (before it became obsolete) but never installed it (now he's lost it).. PreSonus would not sell just the bulb (not cost effective). Hopefully this helps you out if you haven't gotten it fixed yet. I realize it's been a year since you posted this. Feel free to contact me anytime if desired. Larry