(Without benefit of actually owning a DLink):
I'd connect the two routers together via their LAN ports, and disable the DHCP server on one (might as well be the DI704P, since the DI614 is already working well and so best to leave it alone).
Since the DLinks are both administered via connection to 192.168.0.1, you need to be very carefull which router you are connected to. To be sure, leave the routers disconnected from each other, plug a Mac or PC into the DI704P with an ethernet cable, turn off the Airport/WiFi card on the Mac/PC so you are sure it cannot connect to the DI614+ (I'd turn off the DI614+ if it was possible), and connect to the DI704p's admin util at 192.168.0.1 and get the print server working the way you want. Then go to the Home>DHCP admin screen and click the Disable button. (To connect to the DI704p thereafter you'll need to set your Mac/PC to a static IP, since the DI704p will no longer provide a DHCP service to the Mac/PC.)
Disconnect the Mac - DI704p cable and go back to your wireless connection to the DI614+.
Then connetc a LAN port on the DI614+ to a LAN port on the DI704p, and see if you can use the print server.