Short answer to question: Yes, Brahman is beyond all the concepts.
Kenopnishada can certainly help with that and you can extrapolate the fact given there to get understanding of what you are asking. (Sorry, but I do not know IAST, so you can add it but do not remove dev nagri version)
न तत्र चक्षुर्गच्छति न वाग्गच्छति नो मनो न विद्मो न विजानीमो यथैतदनुशिष्यादन्यदेव तद्विदितादथो अविदितादधि |
इति शुश्रुम पूर्वेषां ये नस्तद्व्याचचक्षिरे ॥ 1/3 ॥
Focus on the words न विजानीमो यथैतदनुशिष्यादन्यदेव
it means neither we know how to instruct one about Brahman. This clearly shows that all the philosophies concerning him are just logical interpretation of Brahman, done as per the perception of a person, not what Brahman really is.
Further it also says तद्विदितादथो अविदितादधि
which means he is distinct from known (or what can be known) and is beyond the unknown (or what cannot be known).
It implies you cannot describe Brahman in words because words can only describe generalisations not what Brahman actually is.
The answer written further has a trigger warning: Vedic Darshan (no extensive discussion shall be done in comments about it).
This can, in a generalised form, also be confirmed by Nyaya Darshan of Gautam:
इन्द्रियार्थसन्निकर्षोत्पन्नं ज्ञानम् अव्यपदेश्यम् अव्यभिचारि व्यवसायात्मकं प्रत्यक्षम् ।। 1/4 ।।
Above is about Pratyaksha Gyan (Direct knowledge perceived by 5 senses and Mana) and there is a term अव्यपदेश्यम्
. It roughly means that direct knowledge should always be indescribable. For example, you eat a mango and an apple both were sweet but you can never describe using words what kind of sweet mango and apple were. To be more precise you cannot by telling to someone about taste of them make other person taste them. Both had different taste but taste cannot be described.
This rule of Gautam can be applied there. You cannot even make other person taste something by merely telling him, let alone Brahman.
Since the sages have experienced Brahman they cannot describe it anyhow because that is what Direct knowledge is. Direct knowledge would always be bound in the rules of Gautam.