It'd be good to know what the RT-60 is in the room. A general rule of thumb for hi-fi listening is around 300ms, and fairly even through the frequency band, rising a bit as it goes into the bass.
Absorption is best applied in multiple smaller panels rather than large single panels. Break large flat wall surfaces into smaller reflective zones. Tall, thin vertical panels with a mix of diffusive and absorptive properties are ideal, as their edges will scatter sound more horizontally than vertically. One goal is to break up the fewer strong reflections into many more weak reflections that are spaced apart, averaging about one per millisecond reaching your ears. So about 300 reflections before it fades below audibility. That will ensure an open and lively sound that is very neutral and low in room coloration.