The Obelisk X-2 power supply (in fact, a dual-mono power amp PSU) when combined with the Obelisk Si holds the amplifiers ante at a full unbridled 50wpc, while allowing the original on-board power supply of the Obelisk Si to dedicate itself entirely to its preamp section.
In other words, with the addition of this single device, the Obelisk Si evolves into a fully-fledged dual-mono pre/power combination. It is a substantial technical upgrade, and consequently a leap forward in sonic performance: it catapults the single-box integrated Obelisk into a much higher league. With the X2 combined with the Obelisk Si, the sound-stage leaps forward - with even 'blacker' blacks, more three dimensional imaging - coupled with warmth, poise and detailed precision.
It is not that the Obelisk Si doesn't sound fantastic with it's own power supply - it does as you would expect (as owners and reviewers can testify), but for those wanting to take a smart step up in performance - its a simple and clear choice: a definite performance upgrade. This can be a real world decision, for those that are taking their first steps into pure musical enjoyment by building their first 'proper' audio system, or for those who want a little bit more - but have little real-estate on hand to expand.
You don't have to re-invent the wheel if you love using it, but you can refine it and make it better...time has taught us this, and Heed have applied this simple and reasoned logic with the provision of the Obelisk X2.