Answer
Krishna, the Supreme Lord, is the real "gulab jamun." The gulab jamun prasadam that we receive is no longer material because Krishna accepts it.
Just as the maha-mantra is chanted with a material tongue, yet the Lord enters that sound and transforms it into a spiritual vibration, similarly prasadam is transformed by Krishna's presence. The omnipotent Lord converts an ordinary material object into something spiritual.
In this material world, everything is a duplicate reflection of reality. Krishna's incarnations, however, are not duplicates. When Krishna appears through His name, prasadam, deity, or other authorized forms, the ordinary material medium becomes spiritually real.
For example:
When you chant, the Lord transforms ordinary sound into absolute spiritual sound.
When food is offered to Krishna, He transforms it into prasadam, imbued with His presence.
At present, we may not fully experience the spiritual taste because our consciousness is still conditioned. We are eating spiritual prasadam and chanting Krishna's holy name, but our spiritual senses are not yet fully awakened.
As purification progresses:
The spiritual body awakens.
The spiritual mind awakens.
The spiritual senses awaken.
Then the same chanting that now seems ordinary will reveal its actual taste.
Rupa Goswami explains that when one experiences the true taste of the holy name, millions of tongues are not sufficient to relish it, and millions of ears are not sufficient to hear it.
Therefore, continue with Soulful Japa. The holy name is Krishna Himself. As purification increases, the real spiritual taste gradually manifests.