a 75E dish requires a 75E specific lnb, whether it uses a stacked y-shaped unit, or a dual quad. The LNB will have it's intended dish model marked on it.
for comparison, the local Starchoice designate for my area put my new 75E dish up here, and used a 60E dual quad... I was never able to get good eB/No numbers on both sats at the same time as the throat spacing was different. I had to contact Jasbir at Starchoice to have their shipping dept send me the correct lnb because customer service didn't know what I was talking about and tech support was only marginally better. Once I did install the correct dual-quad, my numbers skyrocketed.
I like the 75E dish a lot more, the mount has jack screws to set the inclination, which is much more precise than the clamp screws the 60E uses - waaayyyy easier to peak the dish that way.