First, note that the word Brahmi is not found anywhere in the Sanskrit verse. It was inserted by the translator.
But, anyway, it's talking about BrAhmi, the foremost among the Ashta Matrika Shaktis. And, "the other powers" are the remaining 7 Shaktis of the group (names of whom are given later in this answer).
We find their mentions throughout Tantras and mentioned in the following verse as well:
MulAshtakantu brAhmadyAshcha-asitAnga-adi-bhairavAh |
Mangaladaishcha mithunair-ashtabhihi shavidatah priye ||
O Beloved - BrAhmi etc. 8 Shaktis and asitAnga etc. 8 Bhairavas
constitute the MulAshtaka. They are known Mangala etc. 8 couples (the
KulArnava Tantram 10.84
The commentator provides the names of the 8 MAtrikA Shaktis and their 8 consorts (Bhairavas) in his commentary and which is as follows:
BrAhmAdyA ---- BrAhmi etc. Ashta MAtrikA Shaktis. They are -- BrAhmi,
NArAyani, MAheswari, ChAmundA, KaumAri, aparAjitA, varAhi and
(He refers to the Brihat Tantrasara, 10th Edition, p-537 for this quote).
asitAngadibhairavAh ---- asitAnga and other Bhairavas. They are --
asitAnga, Ruru, Chanda, Krodha, Unmatta Bhairva, Kapali, Bhishana and
(And for this quote he refers to Purashcharjarnava, 2nd Khanda, 6th
The Asta MAtrikAs, of which BrAhmi is the foremost, are Avarana Devatas. They conceal the true nature of ParA Devi from the SAdhaka. They remain surrounding the Supreme Goddess and have their respective shares of worship in the Yantras.