Either way works fine and has benefits.
Desk:
Using a desk will help all of your channels get the sound of the desk. These things are always cumulative per track so that is a fun way to get there. Also, depending on your channel count and/or patience for bouncing stems through the mixer, you get some analog summing which is nice. You don’t have to do all of the performance on the faders either if you don’t want to. Just animate the sends in your DAW.
If you’re working with a lot of headroom then it won’t make too much difference vs riding faders, or you can work with less headroom and use the DAW to animate driving into saturation. I use an SSL SiX for this sometimes and sometimes an old Tascam 688 if I want some gunk.
If your desc has an insert/send I would probably set up the patchbay so that I could track through the desk as well. That way the signal goes through the desk on the way in and also in mixdown. This assumes I really like the desk though haha!
If you’re going with a vintage mixer it’s good to be familiar with a soldering iron and how to read the schematics. They can be a nightmare but also they are usually pretty simple and straightforward, point to point or big fat traces on gigantic pcbs. If you get one that works and hasn’t been too abused you may never need to get under the hood except possibly to re-cap it.
500:
For processing individual instruments via outboard of any kind in Logic I have a template with sends etc set up and will often put a channel eq on the send so that any surgical or overall EQ is handled before it hits the analog stuff. There are surgical EQs in 500 that are great, but for me I work better if the “problems” are fixed before I send it to analog and then I let the analog stuff focus on the color/saturation/knob-fiddling that I like. You can have a lot of fun doing this, at least I know I do.
For mastering there are a lot of great 500 series items though they are often pricey–two channels. Things I use: IGS Rubber Bands mastering edition, Zähl EQ, any clean Preamp (I am partial to the AEA ribbon mic preamps for clean but the Cranborne’s could do this too if one would rather have a mojo knob than a one-way tilt-ish EQ) for makeup gain, any colored preamp for makeup gain, Serpent for bus compressor ala SSL, Bettermaker Compressor for DAW-controlled VCA compression (mid/side capable as well), I like using a pair of the Electrodyne channel eq remakes–super gentle curves and and the EQ freqs work well for me. I haven’t run any of the 500 optical compressors but they exist. I also tend to shy away from tubes in 500 series (on the mastering bus anyway). Colour Palette/DIYRE offers some subtle and not-subtle saturation options as well.
A person could build a very functional mastering lunchbox in 500 but probably not on the cheap; or maybe it’d be awesome on the cheap because it all depends on the kind of music anyway. Some things I think of as being better in 19" or only available in 19" – nearly everything I master goes through a Tubetech CL2A. But many elements are great in 500 – nearly everything I master also goes through 500 IGS Rubber Bands Mastering Edition.
It’s a great time to be alive and processing audio because all of these things are flexible and sound really good–digital plugins, 500 series, desks, 19", hell even pedals. Use the formats for the parts that make you happy. If you like the feel of faders start with a desk and augment from there. If you like the dials and switches and portability of a lunchbox then start with 500. Let whatever makes your hands happy be the start point and then you’ll use it and figure out where to go from there.
