Hello Everybody: I'm looking for a lightweight arranger keyboard that I can use a flash drive with midi-files and has 128 polyphony. I currently have the Yamaha S910 and the S550. The S910 I great but sometimes too heavy and the S550 only has 62 Polyphony.

Anyone have any Ideas??? I have been looking at The Roland BK-3.

Roland BK5 will fit your needs. Very light, 128note polyphony and plays midi files, wav and mp3 files via the flash drive.
And, if interested I have a BK5 in stock and at very reasonable price!

If you've got a bigger wallet, I highly recommend the BK-9. Only 20 lbs, a full 76 note action (nice if you play piano), and not much more money than the S910, which apparently you could afford.

It has a FAR better action than the BK-5 (and don't even get me started about the S910/950 action... Yuck!) and some seriously better capabilities, sounds and styles.