No worries. Sorry, should have given the health warning on type of midi lead (and beware that I am no midi-expert!)- you need a midi TRS-to-5 pin din lead for the 404. Boss make these; just beware that there are two subtle variations of these, and only one will work- I think it’s the ‘Bmidi’ rather than the ‘A’, but you might want to check before you order- mine’s not clear what it is…
Then connect to a standard 5pin din lead, which will either go straight into the TR8S or you’ll need a similar 5pin din to TRS adaptor - I’m not sure which connections are on the TR8S?
Then settings - my TR6S is largely plug’n’play - don’t think I changed any settings to make it the Master. 404- go into the MIDI tab of the utility menu, and make sure MIDI sync is set to ‘MIDI’. But I think most of the other settings can be ‘OFF’ if you’re only using the TR8S with it.
(Someone may correct me, but I don’t think channel choice is critical if it’s just for start/stop/clock…? Where I do have to take notice of the channels is when sequencing specific samples on the 404 from another device- in my case an OP-Z. Then each bank on the 404- A/F, B/G, etc.) Has its own channel of 1 to 10 (plus 16 for Chromatic mode. But that’s a bit more complex than what it sounds like you’re trying to do).
I use the Sp404 almost as a looper- I go into Pattern mode and set up some blank 4 or 8 bar patterns- to select the first one you want to use (without playing), hold the Enter encoder and press the pad, which ‘arms’ it - then when you press Start on the TR8S, it should start both- then switch out of Pattern mode to play samples, or press record to put samples into your pattern loops. You can come out of Record mode, change patterns and record on another pattern without having to stop either machine- it’s a bit of a clunky workaround, but pretty good- I reckon it’s about one update away from being a very capable live looper if Roland choose to…