Just read your post this morning and an innocent joy arose spontaneously. Indeed, after bringing non-dual to the foreground, the next step is to let go of this subtle grasping of presence and penetrate deeply into the two fold Emptiness.

In many of your recent posts after the sudden realization of anatta from contemplating on Bahiya Sutta, you are still very much focused on the vivid non-dual presence. Now the everything feels ‘Me’ sort of sensation becomes a daily matter and the bliss of losing oneself completely into scenery, sound, taste is wonderful. This is different from everything collapsing into a “Single Oneness” sort of experience but a disperse out into the multiplicity of whatever arises. Everything feels closer than ‘me’ due to gaplessness. This is a natural but as you mentioned in your post,
...somehow, even though luminosity is no longer seen as a Self or observer, there is still a sense of solidity that luminosity/presence is constantly Here and Now. The tendency to sink back into substantialist non-dualism is still strong...

Indeed and very well said. ‘Now-ness, Here-ness’ are no different from ‘Self-ness’, let go of all these. There are several discussions in your forum recently that are related to the pointing out of the difference between the bliss that comes from non-dual Luminous Presence and 'self-liberating' aspect that comes from the insight of two fold Emptiness. You can re-read them, it may help. Also, it is time for you to put aside the Presence, this taste is already implicitly present, rather focus on having direct experiential insight of the following:

1. Unsupported

This experience is radically different from One Mind that is non-dual. It is not about stillness transparency and vividness of presence but a deep sense of freedom that comes from directly experiencing manifestation as being disjoint, spontaneous, free, unbounded and unsupported. Re-read the first stanza of anatta – an excerpt
1. The lack of doer-ship that links and co-ordinates experiences.
Without the 'I' that links, phenomena (thoughts, sound, feelings and so on and so forth) appear bubble-like, floating and manifesting freely, spontaneously and boundlessly. With the absence of the doer-ship also comes a deep sense of freedom and transparency. Ironical as it may sound but it's true experientially. We will not have the right understanding when we hold too tightly 'inherent' view. It is amazing how 'inherent' view prevents us from seeing freedom as no-doership, interdependence and interconnectedness, luminosity and non-dual presence.

2. Unfindability, Corelessness, Essencelessness and Ungraspability

Further penetrate into these unsupported freely manifesting phenomena and look into the core of whatever arises, not only there is nothing behind as a background, there is no inner core that can be found, nothing ‘inherently there’. If we truly see this unfindability, corelessness, essencelesnesss and ungraspability empty nature of the moment to moment of experience, something ‘magical’ will happen. Observe how the karmic tendency to ‘hold’ releases itself when the empty nature of ‘whatever arises’ comes into view.

3. Embrace the view of Dependent Origination

Do not get bounded by the ‘who-where-when’ construct and embrace the view of dependent origination fully; always only 缘起当生, 缘尽当了 (AEN's translation: arises upon the arising of conditions, ends upon the cessation of conditions). Practice diligently until there is the experience of unsupported continuous opening without inner core but do not rush into any experience. :-)

Happy Journey!
Good site about emptiness, highly recommended reading.