I’ve noticed this one of several posts that proposes replacing Maths with the 506 and as an owner of the 506 since pre-order (and an owner of Maths) that I can deliberately say, it is not. I don’t think it’s an apt replacement for quad envelopes either, as the 506 brings pretty unique functionality with its variable duration (and response curve via the expander).
If you are seeking a Maths replacement, I would highly recommend the Frap Tools Falistri. It features an equally confusing aesthetic (upon first glance, it’s actually quite intuitive, like Maths), and several options for polarization and attenuation.
The 506 does feature both AVG and SUM functions in the vein of the Maths mixer, but lacks the 2 channels of input attenuation and polarization that Maths offers. Falistri does offer a 4 quadrant multiplier which matches some of Maths mixer functionality (there is some convenient normalization occurring within Falistri as well, but I don’t want to make this Falistri focused).
If your primary use for Maths is envelopes, then the 506 can in fact replace it, and you’ll get twice as many envelopes. I feel that envelopes are only half the function of Maths and to achieve the attenuation and polarization functions with channels of the 506 using its slew functionality is possible, the density of the controls within the confines of locking and unlocking channels makes it fairly difficult.
Maths isn’t necessarily a functionally dense module in comparison to the 506, not by 2020 standards anyhow, but there’s a reason it’s the most popular eurorack module. A lot of that has to do with its UI. It’s spacious and fairly straightforward in use. 506 is straightforward, like most ADDAC designs, but it’s not particularly comfortable. I also have sausage fingers.