I have lots of EL designs and I agree with most reply's. The designs are very dense and sometimes I think the machine is going to fall apart.
My hoop fields are 4x4 and 5x7, so the first thing I do is look at the stitch count. I can't see doing something with 40 to 50,000 stitches in those fields sizes. I was told to download in DST(i think that's right term) and then convert to ART. I haven't tried this, maybe someone else has.

On the more dense designs I use tear away stablizer with one or two USED dryer sheets. It does not feel as stiff yet keeps it from stretching.

I'm really new at this; so new that I just made my first payment on my Viking Ruby. Just about all of my designs come from emblibrary.com (this is the one you are talking about right). I don't have a problem with any of the ones that I've done. I just made several sets of free standing lace ornaments and then I made a stained glass nativity scene on denium using rayon thread. I used the stabilizer they recommended (med weight cutaway) and it is really pretty. I think that I used the recommended size 14 needle. I'm still learning and haven't taken any classes yet but have found out a few things. One, I have to use the clips for the hoop to make sure the fabric and stabilizer stays tight. Two, if the stablizer is a little small for the hoop, it covers it but when you secure it there isn't enough sticking up to clip it down then I use blue masking tape along one side and then clip it down and it stays in place. When doing the free standing lace and my design messes up and tears my stabilizer I can take my 505 spray and put another piece of stabilizer on it and mend it; then I back up my stitches and keep on going. This step has saved me lots of redos and stabilizer. I'm doing bibs this weekend. I go to thier projects and see what projects use the same fabric as I do if they don't have the one that I'm doing and I follow thier instructions as to what items to use. It's worked out great so far.

I have Brother machines and use the Embroidery Library designs all the time...thread breakage rarely and then usually discover the thread has caught on something. . I have used both the fill and the lighter designs with excellent results. Use Robinson- Anston Rayon threads the majority of the time and stabilizers vary from easy tear away to cut away to vilene. etc. Mostly #80 needle.

I have been embroidering for a few years now. I have two Brother machines (from 4x4 to 6x10) and I have not had any problem. I'm trying to figure out what the problem might be. Have you tried different stabilizers, needles and different threads?
Some machines work better with different brands of both stabilizers and threads. I think you could pick one design and test it changing needles, threads and stabilizers and making notes on what works better for you.
Also, are you using embroidery needles or regular needles?
My two cents.

When my machine starts to make a pounding sound, I CHANGE the needle, it needs to be really sharp and fresh. Stops the pounding of the needle. I like the fine underlay of their designs (Emb Library) they stich out so wonderful. I do pay attention to the number of stiches when I purchase a design because it can take a couple of hours to do 1 design and I am not into that anymore. I have a Janome 200E and a Bernina Artista. I also use a 2oz. stablizer Floriani (spelling) the one that does not have a "give", works out great for all types of fabric.
I use a 90 needle for embroidery ball point for tshirt and sharp for other fabric.

I have the Babylock Ellegante and have not had any problems with the designs. I make sure the jump stitches are set to trim during embroidery. I use the light weight tear away stabilizer sheets, and if there is any wording that will be on the design, I will iron on the stabilizer sheet, but also add another sheet (un-ironed)when hooping to make it sturdy. If I don't do this, the outline stitches do not match with the satin stitching. I do not use anything other than the light stabilizer as I have a hard time tearing the medium or heavy stabilizer. If doing a wall hanging or purse, I will use the heavier stabilizer. The better the stabilizer and the tighter the hooping, the better the design will turn out. I also run my machine at 600 stitches, no higher. Use only sharp Schmetz embroidery needles and good embroidery thread that is not exposed to dust. I also have the Designer's Studio and eliminate some of the dense stitches. They stitch out much better and are not 'stiff'. I do prefer Amazing Designs and have not had any problems with any of the stitching.

I thought about that too, because my Janome 11000 Customizer will enlarge the design, but it doesn't add stitches. That sounds like the best idea.

I also love their designs and have been buying them for years. Yes, they are dense but what
I have found is, I increase the size 20% and that seems to work for me.
If the design is very dense, I will buy the smaller size and then increase it.
Hope this helps.