Argthtjtr

Since the Advaitic Brahman has no qualities - it must be that all these Gunas are obstructions to achieving Samadhi.

Are there Advaitic statements that one must transcend all three Gunas?

For now presenting non-subtle answer only...

Although the door to samaadhi is from sattva as a psychological quality, one has to eventually transcend it according to advaita. From Bhagwat Geeta

BG 2.45: The Vedas deal with the three modes of material nature, O Arjun. Rise above the three modes to a state of pure spiritual consciousness. Freeing yourself from dualities, eternally fixed in truth, and without concern for material gain and safety, be situated in the self.

Here, I think pure spiritual consciousness is nothing but a state of no mind - beyond chitta or samadhi.

Is the Sattva-Rajas-Tamas classification considered important in Advaita?

It is important in Advaita, as well as all Vedantic Sampradayas.

Are there Advaitic statements that one must transcend all three Gunas?

They are not merely Advaitic statements, but Vedic statements, since the Bhagavad Gita says the same thing:

14.23 - He is said to transcended the Gunas, who remains like one indifferent, undisturbed by the Gunas; and who, knowing that it is the
Gunas that are active, remains stable and does not act;

Ramanujacharya's commentary for verses 22 and 23:

One [who is liberated from the Gunas] does not resent the effects of
Sattva, Rajas and Tamas known as enlightenment, industry and delusion,
respectively, when they arise in regard to things different from the
Self which are undesirable; nor does one crave the things that are
different from the Self, but desirable, when they are withdrawn.

He who remains like one indifferent — namely, who is joyful in the
realisation of the ātman as being different from the Gunas and is
unconcerned about material things and is not therefore disturbed
through aversion and attraction and who remains quiescent, reflecting
that the Gunas produce their own effects like illumination etc., and
so remains inactive and does fall under the control of the Gunas.