Jitter 40.000 and "unexpected realtime delay on task 0 with 57000" good enought?

Did you try the boot up kernel parameters?

oh, now i have added the flags, so my call is

BOOT_IMAGE=/boot/vmlinuz-4.19.0-11-rt-amd64 root=UUID=56a0a235-95ea-4827-8f16-5d4340212beb ro quiet intel_idle.max_cstate=0 processor.max_cstate=0 isolcpus=1 noirqbalance

max. Jitter starts then right away with ~34.000 and goes up 38.000-40.000
before this I had a minute ~25.000

have you black listed all the sound modules and disabled sound in bios? This is also another possible latency source.

check to see what is loaded with:
You should probably blacklist them in a file in /etc/modprobe.d

For example I have a file in that dir called "snd-blacklist.conf". It contains these entries:

I have disabled "Onboard HD Audio" in the bios. With lsmod I do not finy "snd" or "sound"

Ok - then you might be at about as good as it's gonna get.

The only things I have found in some investigations I did in getting the best I could out of a couple of machines was:
[1] for some reason the Debian 10 iso gave me terrible results. I did a build using Mint 19.3 and install an RT kernel per this thrread:
forum.linuxcnc.org/9-installing-linuxcnc...nd-easy-installation
and i got a significant improvement. This may have been a quirk of my h/w.

[2] if you really want to get lower latency you might need to consider going to an earlier version of linux with an RTAI kernel. I'm not sure if there is a stable RTAI kernel on Debian 10.

There is of course nothing stopping you trying software stepping with that latency but its not an area I have played in so can't really comment on how things will go.

Cheers - J.

Thank you for all your comments. I have seen also there are mesa cards
store.mesanet.com/index.php?route=product/product&product_id=55
that might fit. If I understand everything correctly.
I need "only" a parallel port for my sherline stepper motor control box
Anyway, this is a new topic Befor this I will do some tests.