At the fundamental level, narcissism and solipsism are intertwined, as the ultimate goal for individuals affected by the former is the desire to return to the infantile state, as reflected by the latter. However, "solipsistic narcissism" outside that state is an oxymoron, as secondary narcissism, as Freud viewed it, is the state in which individuals attempt to reclaim that interconnectedness that epitomized the ego-state of the infantile, which requires the existence of others to unify with oneself. The only state that resembles this, primary solipsism, is only truly achieved at the infantile level, thus making the term functionally impossible for other people.
However, in Infinite Jest, David Foster Wallace offers one way to rectify these "two narcissisms", via the Entertainment, a film that allows the viewer to recreate that infantile state and thus reclaim primary narcissism. By offering a perfect entertainment, one that absolves the viewer of all concerns and instead allows for perfect pleasure, the entertainment replicates the need fulfillment of the mother in the mother-child relationship; at the same time, however, the film ironically is merely a reflection of that relationship, offering need fulfillment while providing none, which leads to the subsequent death of the viewer, who no longer is concerned with his own needs, including drinking liquids.
What DFW demonstrates through this, thus, is that the concept of "solipsistic narcissism" is nonexistent, at least for those in the secondary state of narcissism. However, for the characters, this is not for lack of trying. A majority of the characters in the novel are either beset by addiction, have temporarily conquered addiction with the help of organizations like Alcoholics Anonymous, or have been cast into the void as a result of the external world removing that addiction's source (in the case of Hal). The various addictions in the novel seem to fall into two categories: addiction to some substance or object (what Freud would term object-libido), and addiction to some goal or ideal of self-improvement (ego-libido). In the former, the force of the libido, the individual's sexual energy, is directed at an object, while in the latter, the force is directed back within. Ultimately, however, the effect is the same: to reclaim and empower the self-love that ego represents. This state is best encapsulated in the infantile, where all forces are directed at that ego fulfillment due to the mother's need fulfillment. Thus, both ego-libido and object-libido, as seen through the lens of addiction, are both attempts to reclaim this kind of narcissistic pleasure.
At the same time, however, the fates of the characters indicate that this attempt to reclaim the self-love of the ego is purely destructive. The two characters who encapsulate this are Don Gately and Hal Incandenza, the primary protagonists of the novel, both of whom have used or do use addictive substances to try to escape to that infantile state. In Don Gately's case, he is a recovered Demerol addict and alcoholic who uses Alcoholics Anonymous to cope. While Alcoholics Anonymous, one can argue, is also addictive, it is beneficial in the sense that it forces the addict to liberate himself from the narcissism that addiction has brought on. One of the primary goals of the twelve-step program is the acceptance of and submission to a greater being. This acceptance requires the individual to divert his libido away from ego fulfillment and toward object-libido directed at the greater being. When that libido is returned (through the cathartic gratification of Alcoholics Anonymous and submission to the greater being) that libido is returned, which restores self-worth and ego. Thus, Don Gately's experiences encapsulate the solution to addiction and ego-driven narcissism - acceptance of and association with other people. The relationships built with other people divert individuals away from ego-fulfillment, but leads to that libido being returned, which helps the ego to be renewed. However, Gately's ultimate fate - being given a drug against his will, which renews his addiction - casts a pall over this redemption, and suggests that the journey away from addiction, even with Alcoholics Anonymous' help, is never truly done.
Hal's case, on the other hand, occurs at the other end of the post-addiction spectrum: withdrawal. Having been required to get off marijuana to pass a drug test, Hal finds himself without a source of ego-fulfillment, which the marijuana was. By giving him the opportunity to escape, marijuana helped Hal cope with his alienation and offers him the illusion of need-fulfillment, when in reality the marijuana merely created its own need. As Hal's conscious degrades at the end of the novel and he becomes increasingly incapable of expressing himself, he experiences a reversal - he perceives himself capable of expressing himself normally, but he in reality lets loose with almost primal expressions and sounds. In effect, the loss of marijuana, an outlet for ego-fulfillment, has unleashed Hal's id. Without any stabilizing force that allows need-fulfillment, Hal has ironically unleashed a part of himself focused on immediate need fulfillment, which is where the story leaves him. Most interestingly, Freud emphasized that the id was the state of the infant at birth, which is merely a force of impulse and desire. In effect, Hal has reverted to the child-state, but has been separated from his source of pleasure. One might argue that this lack of restraint from a lack of super-ego, whom Freud associated with the father figure in contrast with the mother's need-fulfillment, indicates both Hal's overarching problem - his father's suicide - and how improper James Incandenza's solution to Hal's problem was. Hal was not in need of entertainment, or a return to the id - he merely needed some reinforcement from the superego, whom James is supposed to epitomize. In effect, by leaving his son to the hands of technology, James' creation for his son may be a source of his internal imbalance and ultimate decline.