I figured out a simple (and much needed) hack to use any installed editor for your comments.
I simply borrowed a block of code from the awesome wiwimod module and pasted it into /include/comment_form.php; that part works well.
For the other part of the hack I could only hard-code the preferred editor or store a selection in a Module preference, so I had to hack each module which uses it.

How do I add a new preference to the system module?
(xoops 2.016)

you'll have to edit modules/system/xoops_version.php

There's some excellent posts on this forum that explain how to add any of the wysiwyg editors to a module, they also explain what you should add to the xoops_version.php file.

Herko