I would agree that your not going to get rid of the venturi on a Lifereef skimmer. That's just the way they are designed. Because they draw air from the collection cup, to prevent collection cup overflows, you can't easily put a muffler on them like you see on some of the needle wheel pump skimmers.
I also would set the Lifereef skimmer up a bit differently. Ideally you want the cleaned water coming out of it to re enter the sump slightly above the water level in the sump. By placing this below the sump level you don't get as clean a level of bubbles. Notice how the level rises and falls in the narrow plastic column.
To get the best results out of a venturi skimmer you really need a pressure rated pump, something like an Iwaki MD55-RLT. The power head type pumps like the mag just can't produce the pressure needed to really get best results out of the venturi. The downside is that a pump like the Iwaki is going to cost a lot more, and consume a lot more electricity compared to a needle wheel skimmer skimmer, especially if needle wheel is using a DC pump. Also, most pressure rated pumps must be mounted outside the sump, they are not submersible. This means doing a lot more plumbing. Notice how the bubbles in the Lifereef skimmer are all different sizes.
You would also get better results if you were using a Mazzei venturi. However it's a lot longer and a lot more expensive.
The bottom like here is that the Lifereef is running at a big disadvantage. However, even if you made all those changes I mentioned above, your still not going to resolve the venturi noise and you need to spend a lot more money to upgrade it and you'd spend a lot more to run it. The Lifereef is a great skimmer, but even with the improvements I don't think it will be that much better than the RLSS.
For those reasons I think your better off with the RLSS.