Vairagya-ananda is an oxymoron. Not quite. It is not uncommon that men with few possessions are happier than those with more possessions.
One of the impurities of the mind is that it is a wandering mind. A wandering mind may not enjoy even if the content is enjoyable. Controlling it is an important spiritual discipline. Arjuna says (BG 6.34) that it is very difficult to control the mind, as difficult as to control the wind. He expects a reply from Sri Krishna who while concurring with Arjuna (like a good teacher) gives a remedy (6.35) that the mind can be controlled by practice and dispassion (vairagya). Dispassion is one of the four qualifications for Jnana yoga.
Everyone wants happiness. A person is happy when his desire for sensory objects is fulfilled. However, it is an obstacle on the spiritual path because desire is insatiable. If one desire is satisfied, another takes its place. Bondage and desire are effectively synonymous. Dispassion is overcoming desire. By satisfying a desire, a person is happy, albeit temporarily. As a corollary, a righteous person practicing dispassion should be unhappy. Surprisingly, Tattiriya Upanishad claims to the contrary.
Ananda-mimansa is one of the topics in the Upanishad. Mimansa means analysis. Brahma-Valli of the Upanishad talks about Anandamaya kosa and Atmananda. Atmananda is Jiva’s real nature and kosananda is the reflection of Atmananda in the mind when it is calm. Whereas Atmananda is permanent and unchanging, kosananda is due to the satisfaction of a desire and is directly proportional to the calmness of the mind. Happiness in higher worlds, e.g., heaven, etc. is also kosananda. The higher the world, more is the happiness there.
One unit of human happiness is the happiness of a good and strong young man of a sound mind and senses, well-versed in the Vedas, efficient in action, and in possession of the worldly wealth. In other words, one unit of happiness is the maximum happiness a man can have in this world. A hundred times that happiness is one measure of the bliss of celestial humans known as the Gandharva. A hundred times the happiness of Gandharva is one measure of the bliss of the divine celestials known as Deva Gandharva. A hundred times one unit of Deva Gandharva is one unit of happiness in the world of manes. A hundred times the bliss in the world of manes is one unit of the bliss of those who are the gods born in heaven. A hundred times the bliss of those who are gods by birth is one measure of the bliss of those who become gods known as karma-devas by performing duties (Vedic rites). A hundred times the joy of karma-devas is one measure of the bliss of the immortal gods. A hundred times the bliss of the immortal gods is one measure of the bliss of Indra. A hundred times the bliss of Indra is one measure of the bliss of Brihaspati. A hundred times the bliss of Brihaspati is one measure of the bliss of Prajapati. A hundred times the bliss of Prajapati is one measure of the bliss of Brahma. Therefore, one unit of the bliss of Brahma is 10 to the power 20 times the maximum happiness of a person in the human world.
The Upanishad says that a righteous person (follower of Vedas) who practices vairagya gets happiness equal to the maximum happiness in this world and happiness in the higher worlds up to the world of Brahma. With the advancement of dispassion, happiness increases a hundredfold. Vairagya is considered special to point out that the increase or decrease of bliss is independent of the type of objects. Though vairagya is glorified, it can only earn finite happiness however big.
In the above equations, Atmananda is not in the race because it is the result of Atma-Jnana and does not increase or decrease.