Here's what I've heard in reference to the Epson's, very high cost for parts, limited techs that can work on these products. Everyone I knew that had the Epson wide format (about 4) has switched to either HP or Canon.
You should also call or least check out Paradigm Imaging for wide format Canons, they are a sponser of the P4P and I would think that the Canon ipf610 is a better fit. Why, because both the HP and the Epson seemed to be geared more towards Graphics Arts, the Epson has 11 inks, the cost to replace all 11 could well run over $1,000. I'm not sure how many inks the HP has however, the Canon has only 5 inks to replace and the quality is outstanding along with a retail price of $2,545.
Consider this also, even if the HP and Epson has finer detail this can only be noticed when you are close to the image. I'll bet if you lined up all three prints from Canon, HP & Epson, no one would be able to tell them apart.
Try changing the rules! I'm sure all of the pictures that they'll get are not going to be digital, and I'll bet if you dig, you may be able to find out that they may have the need for a color wide format copier, scanner and printer. This way they can make an enlarged copy of the photo, if this then becomes a need you have then knocked out Epson and have built the sale to upwards of 16K.
Hope this helps!