Maximum number of auxiliary verbs in one sentence?

[Kuba]

But doesn't that always require a word like "to", "te", "zu"?

I don't think so - e.g. Slavic languages do that complementary infinitive thingy without any "do" or "ku".
He must not not dare to disturb me when I sing.
Er darf es nicht wagen, mich beim Singen zu stören.
Niech się nie ośmiela przeszkadzać mi w śpiewaniu.
?

[''']

But Dutch, being germanic, is more prone to such use.

[polishboy]

chciałbym móc chcieć potrafić musieć pić.

[Travis B.]

One thing that should be noted that is this question includes the use of pseudomodals in English, there then is really no limit on the maximum number of auxiliaries/modals/pseudomodals in a given clause in English.

[TaylorS]

@KingHarvest: Can you explain what a complementary infinitive exactly is, please? Haven't come across that term yet.

An example of a complimentary infinitive in Spanish: Tengo que ir
In English I want to see the movie.
In German:
Ich will ins Büro gehen.

In my speech "see" is analyzed as the main verb while "want to" is the grammatical particle "wanna", which modifies "see."