Be careful using a simple mixer into a laptop, as modular signals tend to be rather ‘hot’ compared to line level. For intance Sam’s performance VCO outputs ~12Vpp (at least in the case of my ones, YMMV) whereas professional equipment Line Level is ~3.5Vpp, and consumer gear is even lower again.
If your looking for a Eurorack master line output module with headphone outs Befaco make one in DIY that you can buy from Thonk (https://www.thonk.co.uk/shop/befaco-output-module/) although there are probably a load of others that I haven’t spotted.
The line-in stages in professional gear tend to have a lot of headroom (often +24 dBu, which is over 30 Vpp), and a lot of consumer audio gear has no trouble dealing with hot signals either. So for active audio devices, odds are you can just plug things in directly and attenuate via gain/volume controls (but make sure to dial everything down before plugging things in).
I’d be more careful with laptops and headphones, though. For line input, the simplest possible attenuator is just a pot & two jacks, see “simple attenuator” at http://www.doepfer.de/DIY/a100_diy.htm for how to wire things (you can replace the pot with two resistors, e.g. 2k2 and 1k0). For headphones, a suitable amp or module with a dedicated headphone output (and a dedicated volume control) is probably your best bet.
This is 2 simple mixers stacked for 8 stereo channels with independent pots for left and right. Works great for me. Zero issues with plugging it into my Mbox 2.
XLR connectors are quite common for professional sound and lighting gear. I’ve been considering adopting 4 pin mini XLR for power distribution, as an alternative to the usual Eurorack ribbon cables and headers. I find it crazy that some people are spending hundreds of pounds on a module but then connecting it to power using reversible headers.
The module can also be wired for jacks. You’d be using stereo jacks to carry a balanced mono signal. I actually put both XLR and ¼” jacks in mine. And the PCB was only, like, $13.
reversible headers ? you would have to try real hard to reverse these , they are slotted and have an arrow on them that is always negative side and ribbon cable has red stripe on negative side . which I honestly don’t get why they did it that way , positive is usually red [ like cars ] .
And arrow is usually positive. Some Doepfer stuff is just weird.
(Someone should really clean up their Wikipedia page, btw (which I only looked at because some MuffWiggler referred to the company as Döpfer). The article doesn’t even mention Eurorack or their impact on industry, but it has what appears to be a list of everything Dieter’s built from 1979 to circa 2012 ).
“by the way” – used for “something that relates to the subject you are discussing, but is not the main point of the discussion” to quote a random dictionary.