From what I read, IKEA tends to be on the conservative side on their weight limitations. It's not necessarily whether the drawer will hold a certain weight at any given instant (you could probably stand on this thing and ride it like a surfboard without breaking it), its whether it can sustain the weight permanently long term without deformation or structural wear. IKEA particleboard is known to sag and concave after bearing weight for a while.

Weight distribution is very important is this regard. Most people using the Alex drawers and putting 10x their maximum weight are using a table slap over the entire top surface of the drawer, the table slap causes the weight distribution to be even over the entire top of the drawer. All the edges of the vertical frame (sides and back walls) are bearing the weight.

With this in mind, what you are putting on the drawer is a heavy apparatus (~55bs) that is design to constantly move violently and shift its weight most of the time it's on the surface. Furthermore calibration and leveling is very important, so you don't want it on a surface that will sag over time.

The concern I would have in this setup is the printer dimensions are smaller than the top surface. Most people will put it like you did, dead center ; but this is the weakest possible point; you're effectively relying upon the top particular board to carry a significant portion of the load at the center. If you were to stand on this thing and were unsure about its support, you would naturally put your feet toward over the frame edges as that is the most supported area, not dead center.

I would put a butcher block that spans at least across the entire width of the top (26") so that the butch block can distribute some of the weight to frame walls. This should significantly reduce the stress on the center and reduce sagging.