Logic Masters Deutschland e.V.

This is a normal Sudoku-grid.
Except, the digits are letters, instead:

Eight knights chat
about one thing.
In this array,
they don't see their kin.
Amongst them, flat,
lies dead a king.
Just passed away.
He was cross about sin.

To solve this conundrum,
start to think!
Do not cede and abandon -
you will need some more ink.

That's all for now -
enough of me yacking.
What's the use anyhow?
Let's get cracking!

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Addition:
Something about this riddle confused
either the setter or the software he used.
If you use the conflict checker in SudokuPad,
turn it to "Classic Sudoku" instead.
---

To check your solution replace I with 1,
N by 2, I think, you get the idea, just carry on.
E becomes 3 and falls from belief,
H must be 4 - what a relief.
S leaves, 5 comes to pick up the slack,
G needs a 6 and they never look back.
Swap T and 7, as last but one,
K's left with 8 - the challenge is won.

And if all goes wrong,
please, do not panic,
my peers!
Keep seeking along,
there's a strong need for Tonic.

Cheers
; )