As I said I'm not quite sure where he was going with that (he will have a good reason) but it certainly indicated the unit is fine without the tubes in so it rules out a bunch of possibilities, though tubes can fail, they tend to just get mushy over time.. Fingers crossed it's just tubes though. Tube selection is a big topic here, focused though on ADA preamps MP1/2 MB1.
Have a read of the tube topics (http://adadepot.com/index.php?board=38.0) and lots of other posts here to get some ideas for tubes, the EHs would be later on my list, not that they are crap and will work fine, just IMO there are better choices for MP1/2 etc, but it's very (very, very) subjective, personally, I would have gone for the Mullards (long or short plate), MJMP probably the JJs, and boogie STRs (typically re-badged JJs) work very well in MP1 (in my personal experience). And if you want it to sound MP1 stock, the closest to the original Chinese tubes are probably the TADs (from SCs experiences and posts).
While all 12AX7 tubes are to some extent electrically equivalent (the pins you plug them into and the circuit doesn't mind so they work fine), they all sound different. You've gone with the EHs, they will be fine (hope it gets it working i.e. is just tubes..) and hey you may prefer them, some do.