Your hardware has a clock that controls how fast updates to the AO occur. That clock can only have one value at a time. I will let your contemplate the complications that come up with two different clock settings being active at the same time (see below).
So how do you work around this complication?
You will have to develop a single VI that OWNs both output channels. That VI will have to accept start,stop,configure, etc commands from the two clients (what you will have to convert your existing VI's into). If you decide to place a restriction on the services you provide to the clients along the line of "only one sample rate at a time" you will be making your li fe much easier.
If I was contracted by a customer to do what you have asked, I would try to combine the two existing VI's into one or simply buy a second 6110 and avoid all of the hassles. Both of these approaches would end up saving the customer money in the long run while freeing them of any restrictions that where established in order to develop the "server".
I also have the same problem ,and I m using labview 7 with pci-6052 wher two analog output are available .I want to analog out the simultaneous signals to two DAC'S at the same time.how it is possible .