I've had one of those Saleae clone LAs for years. It's cool, it works.
SO why are you messing about with a DS1054Z?
But the scope is supposed to be able to do that.
Says who?
The DS1054Z decodes serial data perfectly, just not in the way you expected it to.
The limitations are no secret. There's a hundred posts and entire threads on here dedicated to them.
eg.
https://www.eevblog.com/forum/testgear/ds1054z-rs232-decoding/Considering the Siglent SDS1104X-E is able to do the decoding properly
Says who?
a) It might not do what you think it does, either.
b) Twisty knobs and buttons are simply the wrong paradigm for large amounts of serial decoding. eg. Setting up serial triggering or searching for data in along transmission is a couple of clicks on a PC but a total pain in the ass on an oscilloscope. That's
ANY oscilloscope, not just a DS1054Z.
(unless you get a super expensive one with mouse/keyboard, obviously).
Bottom line: Use your scope's serial decoding feature to make sure the signals are present/correct. Use your $6 USB logic analyzer to process/decode large amounts of data.