The paq'batlh contains the sentence {Qo'noS tuqmey muvchuqmoH qeylIS} (p.179) implying that we can use {-chuq} with {-moH} to reflexively refer to the subject of the main verb (which has become the object of the verb with {-moH}).  Do we have other evidence of the same?

I don't think that implication is inevitable. The object of the sentence is not "the subject of the main verb." The subject is the subject, and the subject in this case is the causer. We've seen other sentences where adding a -moH doesn't change the role of the object at all.

There are other ways to interpret this. I think that Klingons don't see their sentences quite as mechanically as you're making them. I believe the scope of -moH is variable. Sometimes it applies directly to the verb, and sometimes it applies to the verb plus its object-affecting suffixes. In this case -moH means Kahless is causing the houses of Kronos to muvchuq, not just muv.

I think it's significant that The Klingon Dictionary doesn't usually distinguish between direct and indirect object, and that verb prefixes can sometimes agree with indirect instead of direct objects. I think Klingons see the position before the verb as the "object" position, not necessarily the direct object position. Sometimes indirect objects belong there. Sometimes they don't.

Don't try to "subject of the main verb" this sort of thing. I don't think that's how -moH works. The subject remains the subject, whether it's causing something or not. It's just that the exact meaning of the object is fluid. It might be the thing performing the bare verb, or it might be the thing the bare verb is acting upon. Which one it is must be inferred by the listener.

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SuStel
http://trimboli.name