Within the Islamic tradition as a whole, the Prophet Muhammad and by extension the Imams within Shi'ism - may peace and blessings be upon them - are the premier foci of devotion whose remembrance is inextricably intertwined with remembrance of Allah. The Prophet Muhammad, as you are well aware, possesses not only a historical and personal reality, but also a cosmological and metaphysical significance within the anthropocosmic vision of Islam.
In my opinion ... within the context of the doctrine and method of the [Maryamiyyah] Tariqah as transmitted by Shaykh Isa, much of the significance traditionally and exclusively afforded to the Prophet Muhammad is assimilated into the person of Sayyidatna Maryam. There are several reasons for this which may be identified.
For instance, the Prophet is depersonalized through identification with the abstract principle of the Logos and the personal relationship with him is replaced to a certain degree by vicarious participation in Shaykh Isa's personal relationship with Sayyidatna Maryam who is also considered a feminine manifestation of the Logos. He experienced intimate tantric visions of Maryam and as a result believed that he, and by extension the entire Tariqah, had been blessed by her. He also produced numerous poems, litanies, and paintings inspired by her including a Maryami Wird ...
A second level of assimilation of the significance of Muhammad occurs through the spiritual identity of the faqir with the religio perennis within the context of the Islamic form. Under Shaykh Isa, fuqara were taught to emulate his functional identity with universal metaphysics and the religion of the heart while eschewing the limitations and prejudices of individual religious identity. As Maryam is considered the prophetic embodiment of the religio perennis while Muhammad is limited to the Islamic form, she is given a certain functional precedence as a result.
Within [certain branches] of the [Maryamiyyah] Tariqah, virtually all of the Maryami devotional elements have been rigidly excluded and something of the distinctly Islamic identity has been restored in addition to the emphasis upon the spiritual significance and centrality of devotion to the Prophet. Practically, the only Maryami elements that remain [in those contexts] are the recognition of Sayyidatna Maryam as something of a patron saint of the order bestowing a subtle emphasis on aesthetics, the optional recitation of the Salatu'l Maryamiyyah, and certain doctrinal expositions found in Shaykh Isa's texts.
Something of an answer to your question may be obtained by examining the role of additional litanies historically appended to the Wird within the Shadhiliyyah heritage. The role afforded to the Salatu'l Maryamiyyah within [the Maryamiyyah] has traditionally been filled by the recitation of the Salatu'l Mashishiyyah within the Darqawiyyah, a powerful litany in praise of the Prophet of which the former is derivative. Within the Alawiyyah by contrast, the Wird is preceded by the recitation of Surah al-Waqia.
Of course, [within the Maryamiyyah Tariqah] the Salatu'l Maryamiyyah is [considered] entirely optional, just as the special appreciation of a pre-Islamic Prophet is entirely a matter of personal affinity. I have always been specially attracted to the Prophet Idris, for example, but not in such a way as to detract from or even affect my profound love for Muhammad. There is certainly nothing to keep you from employing any of the other famous litanies that are part of [the Shadhili] heritage instead of or in addition to the Salatu'l Maryamiyyah such as the Burda of Al-Busiri, the Dala'il al-Khayrat of Al-Jazuli, the various litanies of Abu'l Hasan Al-Shadhili, or the aforementioned Salatu'l Mashishiyyah of Ibn Mashish. The Shadhili tradition is vast and beautiful and I believe that only good things can come from exploring it and connecting with it.
For a traditional Islamic Interpretation of Sayyidna Isa and Sayyidatna Maryam, see Mary of the Soul and Jesus of the Heart. For a thorough exposition of the Shadhili Heritage see The School of the Shadhdhuliyya Vol. 1 & 2.
Greetings of Peace. This blog contains selections from my correspondence and other sources on a variety of subjects related to religion, philosophy, and spirituality. I hope that they may be of benefit to the interested reader. Concerning the title of the blog, read this entry.