The chance of getting a modern SSL connection with Win-XP's built in SSL libraries is pretty low.
For classicube.net's SSL you need:
TLS1.0 or higher; this probably needs to be turned on by default (A regedit setting)
SHA256 for your certificate ... I don't think Microsoft ever did this on pre Windows-7
The second one needs specific updates to be downloaded and even on W7 it's temperamental, fragile and reportedly incomplete. So even though SSLlabs says the protocol is compatible, I think you'll find the connection will fail.
I think Cloudflare requires SNI though ssllabs doesn't mention this; if it does you're stuck too.
Using the OpenSSL or similar libraries would work on old windows, but that's likely a major change.
Using an Stunnel proxy at the client end might work though.