Meridien systems don’t support MXF. You don’t want a Meridien system anyway, they’re old and outdated (but still workhorses for SD work!). Go with Media Composer. The additional features (more DNxHD support, paint, animatte, improved shot stabilization, etc….)
I believe you can go with the software only version, transfer the MXF files via Consolidate (or do it as a normal file transfer from the desktop level), transcode to DNxHD for better playback and edit away. As far as monitoring goes–I’m not sure, but I’m thinking you will need the Adrenaline with DNxHD board for that–if you do have that you can capture HDSDI uncompressed directly into your system and it will transcode it to the DNxHD codec of your choice for editing. Avid doesn’t support DVCPro HD natively, I think. Check with a reseller to be sure.
My opinion–do a test run on a MC Software only version (preferably on a beefy HP8400, Avid certified) and see how it cuts and handles the footage. When you’re finished, rent an Adrenaline box for the online or step up to a Symphony if possible. You’ll save on costs (an Adrenaline box with DNxHD board will set you back a lot of money) and you’ll get a better end product (you have to go to Symphony for Secondary color correction anyhow). My opinion, for what it’s worth.