SqueezeCenter CustomLibraries (Installation on Synology DS)

Hello experts,

I am struggeling here since almost two hours. Need help.

Current setup:
Synology DS214+
DSM 5.1-5022 Update 5
Logitech Media Server Version: 7.7.3 - 1375965195 @ Mon Aug 19 11:42:55 PDT 2013

What I would like to do:
Install CustomLibraries beta (by Erland Isaksson) via LMS extension downloader as recommended
(http://erland.isaksson.info/download...ustomlibraries)
Remark: I know, that there is also the older method using various plugins (multilibrary, custom scan, custom browse), but this seemed very complicated to me and I absolutely could not find out, what a lifetime license would cost. I am willing to spend 15 EUR for a working solution, but not 40 or 50 EUR. That's why I am interested in the plugin Install CustomLibraries.

Where I got stuck:
In the LMS Plugin Tab (I guess this is the extension downloader), I do not see CustomLibraries. I flagged that also other plugin should be shown (german: "Alle Plugins anderer Hersteller anzeigen").

EDIT:
One step further: I saw that the extension downloader is actually a plugin. ok. Next problen: In the moment I click on settings, I receive the follwowing message on top of the plugin tab "Falsches Repository http://www.mysqueezebox.com/public/plugins/logitech.xml - Timed out waiting for data" ("Falsches Repository" means "Bad repository"). If I enter the URL to my browser, I get "504 Gateway Time-out". What is wrong here?

What do I have to do to install CustomLibraries on my Synology DS?

Thanks very much in advance
Jacob