Should these e.max veneers be replaced? Could a better result be achieved using a different translucency and/or shade?

I think you would have had a better result with more veneers.  He/she did a good job, but two is not going to look perfect.  If you want perfection, consider more teeth.  Good luck. 

There are so many possibilities that your dentist or the lab can do. HT veneers can be darkened by using a darker cement also. Not sure what shade of cement your dentist is using. The value and chroma of the veneers should be taken into consideration as well. If your dentist is an experience do cosmetic dentist then he should and will take a lot of photos and communicate with the lab he used. Have you ever thought about whitening your other natural teeth around the new veneers more? 

Hi there.  It's great that your dentist is willing to work with you.  Translucency does mean that they will look more grey, but you won't know exactly how it will look until you actually remove these, they make the new ones, and you try them on.  At this point if you decide to have them redone then you should also consider talking to the lab technician about the shade too, that way they can understand exactly what you want and look at your teeth in person and take notes so when they make the final veneers again, they can do their best job with their new notes.  make sure that when you have them tried on again you look at them under different lighting, and by a window if you can. They will always look different in different light.  

I agree with you that the veneers are a little too opaque compared to your natural teeth. Choosing an emax translucency is a difficult process, and the decision is usually made by the lab. Of course on a difficult case it needs to be a discussion between the dentist, patient and lab. The translucency used on the emax ingot depends on several things - prep design, underlying tooth color, and color of your natural teeth. So without seeing the prepped tooth with the veneer off it would be difficult to say for sure.
You have two options to increase translucency for a new set of veneers. For one, you could just use HT emax, but that could lead to a grey edge. The other option would be to use MT again, but have the lab cut it back and layer on a more translucent porcelain over the top. Cutting back and layering is standard procedure for veneers. Either one could be the right option for you depending on the prep design and underlying tooth color. Good luck!