I've read Siels in general are not very reliable so check it out carefully. I tried an Opera 6 once in a music shop and it sounded great (not sure which version), I was tempted but couldn't justify it. I've got an EX80 expander module which is rather like a Korg Poly 800 (paraphonic) but has the benefit of being editable with CCs. One aspect of Siels I really like is that they used SSM filters which sound fantastic.