Spry is similar to MooTools, WEB 2.0 aka: AJAX Framework.
The J in AJAX is JavaScript
Web + Local != easy.
If I read the OP correct you are wanting to request the XML file from a local system to upload to the site the local system is viewing without user interaction.
EG:
Me->YourSite->Requests File->Me->YourSite->Process File->Show Results->Me
Instead of
Me->YourSite->Me->Clicks Upload File->YourSite->Process File->Show Results->Me
Every security measure possible is taken to prevent the first simply because of the amount of malicious developers out there looking to compromise your system.
Thus requiring the user to agree to and install an application to make things work (this used to be capable with out confirmation *shock*)
Imagine you have your resume, address book, emails, ip address, etc stored on your PC.
By allowing JavaScript access via a browser, if you were to go to a website that had malicious code or an advertisement that contained malicious code, what someone could do with the found information? Malicious advertisers already make a fortune on stealing video game accounts by exploiting flash on the targeted video game's help websites. As well as even stealing credit card information from other websites just by recording keystrokes.
This is where Flash, comes in and why it's currently one of the major exploited programs by malicious developers. EG: a malicious programmer can have a flash advertisement record keystrokes, retrieve system information, cookie/session states, copy clipboard contents, and in some cases even execute remote files granting someone access to the affected PC.
http://www.symantec.com/connect/blogs/next-generation-flash-vulnerabilityhttp://www.symantec.com/connect/blogs/analysis-zero-day-exploit-adobe-flash-and-readerThe list goes on..
Another type of exploit is XSS where a malicious user injects malicious code into your website giving them details about your users, access rights, cookie theft etc. That is one reason why AJAX isn't designed to request data from 1 domain to another.
Your best bet for retrieving Local data to serve to the web without explicitly clicking browse -> select XML file is JAVA(not script) IMHO.
If clicking browse or the file is already uploaded to the server then an AJAX request should be fine.