does it come with any software, or docs

you usually select mpu-401 in the game

Problem is that this card does wavetable, and by default, the internal syntesizer is conected to the onboard MPU-401...

I thought the SB128 had no midi synth of its own at all, and relied on Microsoft Synthesizer for that in Windows?

Unfortunately, I don't remember a Midi out / MPU-401 out device when I used to try this card. This is a very budget card mind you they might have stripped that functionality out by chance. If there's a synonym for "defectivebydesign" it's Creative.

SB 128 PCI is based on Ensoniq PCI, as far as I know... Wave-table works on DOS (pure DOS, not only DOS windows in Windows itself). And, as I said, in Windows I can select if use internal synth, or external (through joystick connector), and the CM-64 worked using this method... But I want to use it in pure DOS.

The SB PCI128 is pretty much a rebranded Ensoniq card. It uses 2, 4, or 8MB ECW patch sets for software wavetable synthesis in DOS and Windows.

You may be able to specify some parameters to the DOS drivers to use the external MIDI port instead of the wavetable synthesizer. I don't remember if I ever tried that or not in DOS at the time that I had that card, since the only external synth I had back then was a MIDI keyboard.

If your computer has ISA slots then you may want to just buy an SB16 from eBay for $5 since it provides an MPU-401 compatible interface through the joystick port with no drivers required.