I am 100% with Eileen on this one. Stick to the GENUINE Yamaha Expansion Packs which are FREE to you.
Loading them is not difficult, and you'll get plenty of help on here.
BEGIN by loading the latest version of Yamaha Expansion Manager on to your computer.
Check out the many packs available FREE on their global website.
Don't be confused by Expansion Packs, and Styles. Expansion Packs are packs of ready made styles in a particular genre. For example "Christmas Organ".
Styles are single styles. However.... you load and use them quite differently.
As to storage ....the Genuine Expansion Packs will download directly to your keyboard.
But Styles are best kept on USB sticks. That way you can use them or change them straight away.
Don't be tempted to go and buy massive 128GB memory sticks. 16/32 Gb ones hold massive quantities of styles.
I've got a 16GB one here with well over 50,000 styles on it, and it's still got 13GB free space !
Grab yourself a couple of decent quality 16Gb or 32GB Flash Drives (memory sticks) so that you can download styles directly to them. In this way you can simply plug them into your SX900 and use the new styles atraight away.
Pretty well all of these "Bargain Packs" on Fleabay are nothing of the sort. They are just compilations of completely FREE STYLES which you could download yourself. Indeed, you could probably put together over 100,000 styles in one day from this site alone . Many of these rip off compilations have duplicate listings, and many are of very dubious quality. Your PSR-SX900 deserves better ! You might think they are a bargain......They aren't.
ALL the Tyros styles for example are available to you, as are pretty well all previous older Yamaha keyboard styles. There are also many many compilations, Gig collections, Player Collections, and many others.
There's also many other sites on the internet where styles are freely available. I have one in Germany and one in France whic are worth a look.
Go to the Styles, Registrations and Player lists, and you'll find more than you will ever need.
Also, you can in a lot of cases convert styles from other instruments quite easily. Roland and Ketron are amongst many that I own.
Save your money...Lots of help here .
And Finally. DO become a Member of the site by making a small contribution. You will get so much more from it, and you'll be able to access all of its amazing content as a full member. THAT is money well spent.