I had the Gen 1 unit briefly and didn't like it that much. Sound was very two dimensional and flat. There was also some edginess in the upper octaves which could come across as harsh. Needless to say, I returned the unit and eventually moved on to the Rogue 99 which I love.
A few weeks back, I managed to pick up the XSP-1 Gen 2 for a steal as I too was curious about "improvements". Right off the bat I could tell that the sound was smoother. Bass was nice and tight and the edginess which I'd experienced the first time around no longer existed.
In comparison to the Rogue 99, the soundstage is smaller but the XSP-1 demonstrates better control of bass. Overall, I'm very pleased with the Gen 2 unit and have been using it for a month without issues.
Some quirks; the VFD display is too dim even at its brightest setting. The markings on the front panel are a dark grey on black, which makes them practically unreadable.
