The Xtreamer DVD is nothing more than an old Realtek 1073 based media player with DVD drive stuck on it. It certainly does not do Airplay and is unlikely to do high res Youtube if at all.
Here is a list of devices with (reverse engineered) Airplay which wont guarantee full compatibility, DRM free media will work and some streaming video sites will work but not always 100%.
1) Pivos XIOS
2) Boxee Box
As you can see it's a very short list, neither will play commercial DVD discs. The Boxee Box is no longer supported and the Pivos XIOS which runs XBMC is still in beta though is the better option long term.
The other long term option is wait for Sigma Designs (people who make chip that powers WDTV & others) port of XBMC to their chips, their version of XBMC will play commercial DVD discs (don't ask why super technical/legal stuff). However you probably wont see any products until 2013.
The only other option for XBMC is a HTPC like a Pulsebox
, uses Openelec and plug in a USB DVD drive which should work might want to ask them first just to be safe.
For the AppleTV you can do this, use MKV2MP4 to turn your H.264/MKV into MP4 quickly without converting. Use AVI2MP4 to do the same for XviD/AVI (MPEG4 is part of MP4) and iOS devices will play MPEG4/MP4.
Now get your iPhone or iPad set the Airplay output as your AppleTV and install a basic DLNA client on it like DLNAapp, when you play media it will go straight to the AppleTV.