I have very questions about X2 and XENPAK transceivers:
1) Can i connect a X2 trans with Xenpak trans?
2) Can I connect a X2-CX4 with Xenpak X2-LX4?
1)X2 and Xenpak optics differ in form factor only (X2 is a bit smaller). You can connect an X2 to a Xenpak as long as the optics are of the same transceiver type. Both have SC connectors (less the X2-CX4 which uses InfiniBand connectors).
Note that the newer LRM specification (Long Reach Multimode) is only available in X2 format. However, LX4 (4 x 2.5Gb wavelengths) is available as both X2 & Xenpak.
2) No. The X2-CX4 (IEEE 802.3ak) module uses CX4 cable (copper) whereas the X2-LX4 (IEEE 802.3ae) uses multimode fibre, either 62.5 or 50 micron.
Hope that helps...