The Sambhogakaya is a bit more obscure than the other kayas; it’s like the Holy Spirit in that way. (You don’t tend to hear a lot of talk about the Holy Spirit.) So here I’ll try to connect them, just my own speculation.
In general, the trikaya teaching is a way to explain a Buddha's experience of being. There is the apocryphal story of how the Buddha found his name. Seeing him shining brightly on the road, a man asked him what he was -- a god, a wizard, a man? “No,” said the Buddha, “I am awake." What did the man see? And what was the Buddha feeling?
Being/Sat/God/Dharmakaya can be understood as the formless groundless ground, the "empty witness" without attributes that is behind or primordial to appearances, as the Origin or Source. But that description is not complete because it lacks dynamism, intent, feeling tone, life. If we conceptualize God as solely that then the materialist's argument against Him has traction -- because how could such a complete nothing be effective in any way? But the Dharmakaya, like the vacuum state, has an energy associated with it, the Sambhogakaya. You can get something from nothing because the
actual nothing is more than the
concept nothing. If the ground of being is not material, then “nothing” cannot be a mere absence of material. It is something else, with its own being. This energy can be understood as the natural expression of the fundamental emptiness itself, of its being.
The Holy Spirit is associated with this energy as the creative energy that impregnated Mary. This is how Jesus was both the son of man and God. God the Father, Dharmakaya, emanated a Son, Nirmanakaya, through the intermediary of the Holy Spirit, the Sambhogakaya. As an incarnation, a gross form in our dualistic world, Jesus was a Nirmanakaya (tulku/Rinpoche), but his Consciousness/Chit/Sambhogakaya was an energetic expression of the Father, the Dharmakaya.
Buddha was similarly a Nirmanakaya, an incarnation or embodiment of the Dharmakaya. At the level of expression or message or transmission of the Buddha, we speak about
bodhicitta (awakening-mind). Bodhicitta is known for its compassionate warmth, but it is rooted in the absolute being-knowledge of the Dharmakaya, which is utter absence of limitation, restriction, or suffering. Bodhicitta is symbolized by a lotus, which begins in the mud and then sends a shoot up through the water, blooming in a pristine, stainless flower.
The Sambhogakaya is especially related to symbol. Normally we think of symbols as pictures that we invent to refer to actual objects. But it would appear that there are natural symbols that are not merely conceptual fabrications that illuminate gross objects, but those which naturally arise directly from the Dharmakaya as expressions of its qualities.
At a deeper (that is, more subtle) level than their Nirmanakaya manifestations, both Buddha and Jesus are symbolic expressions of the Dharmakaya, though in different ways. Where the Sambhogakaya of the Buddha was a presence of profound peace, scintillating intellect, and a glowing, blissful brightness, Jesus was like a bolt of lightning that connected Heaven and earth, a shocking transmission of knowledge. The beginning of Valentinus'
Gospel of Truth states it this way:
The gospel of truth is joy to those who have received from the Father of truth the gift of knowing him by the power of the Logos, who has come from the Pleroma and who is in the thought and the mind of the Father; he it is who is called "the Savior," since that is the name of the work which he must do for the redemption of those who have not known the Father. For the name of the gospel is the manifestation of hope, since that is the discovery of those who seek him, because the All sought him from whom it had come forth. You see, the All had been inside of him, that illimitable, inconceivable one, who is better than every thought.
Think of how different the conditions were where Jesus taught. The Buddha appeared in a place and time uniquely suited to his transmission, and he found his place immediately as a culmination of existing teachings. On the contrary, Jesus, while a fulfillment of prophecy, was both a great joy but also a terrible affront to those who "did not know the Father."
So where is bliss in all this? This is the feeling-tone of the energy of this transmission, which is beyond merely feeling good. The fact that we don't associate bliss with crucifixion gives some clue to the special meaning of that word as it applies to the Sambhogakaya. This special meaning becomes most clear when we add the fourth Kaya, the Svabhavikakaya, which is the union or experience of them all together, and also the essence, the single meaning. That meaning is pristine purity: The profoundly simple, ever-fresh, brilliant isness of form, which never impedes the infinite, spacious peace of being. The crucifixion is a testament to the difficulty of living that view and also shows that it is possible.