There's no 'audio' looper on the Roland BK-9. The Chord Sequencer is a MIDI feature. Although, in practice, you might think them somewhat similar, one of the things an audio looper will do is loop YOUR playing, but a Chord Sequencer only loops the chords that you played (and you can still determine style, fills and Variations after it is 'recorded')

On the whole, if you are doing ambient, trance, that sort of thing, you are looking more for a keyboard that uses arpeggiators rather than an arranger. Sure, you can do somewhat similar stuff with arrangers (on the surface), but part of modern electronica's sound is the use of complex arpeggiators.

The BIG difference between arps and styles is that and arpeggiator plays what you play, whereas an arranger looks at what you played, and then tries to interpret it as a conventional chord type. And then plays THAT, not what you played..!

It's a subtle, but important difference.

But if you are determined to go with an arranger, I'd probably go for the one with a sampler on board. That makes it the Korg's (Yamaha's Tyros sampler is useless, as you can ONLY put Yamaha content into it - there's no multi-sample import at all). Plus Korg's voice editing is more in depth and WS-like than most arrangers.

However, the BK-9 might also be a good choice... It has a HUGE choice of synth sounds and pads (but with more limited voice editing than the Korg's), but the thing that puts it over the top is the ability to play audio loops in sync with the arranger, so if you have a library of trance or ambient loops, you can incorporate these easily into your performance. The sky is the limit when you start to add audio loops!

On the whole, I think, if I were looking for something to make this kind of music out live (if you are shooting for at home only, or in a studio, there are a plethora of VSTi packages out there FAR better than any keyboard made) I would make my choice between the Korg PA900 or the BK-9. And, truth be told, I'd probably pick the Korg (even though I'm a Roland user!).

Best of luck.