If you just want the 4 line inputs, and not the mic modification steps, then this version 2 video seems simpler, and while having the H2 but not having tried this, looks reasonable from an engineer's perspective with 4 new line inputs attenuated ~20 dB feeding the deck's mic input preamplifier at a safely reduced level:
http://www.youtube.com/watch?v=N1vJq13ukrkBest low noise/frequency bandwidth is to directly feed 4 line inputs to deck's
mic preamplifier outputs (not inputs as shown) likely involving trace cutting or lifting preamp's output signal at some component path point inserting the shown switches at LINE level (not mic level as shown) points. 20 dB attenuation is not needed in this case but suggest using 6 dB reduction anyway using 10k ohm values for both R1/R2 and not any of the 100 ohm values used for Mic Level modification.
However, likely need the H2 repair manual having circuit diagrams and a lot more optical/microsoldering tools and soldering technique making it impractical for most to attempt. But this allows the very best audio performance from the H2's 4 track mode, and
might be worth all that extra trouble.
Might someday attempt this myself already having all the right stuff, and finding the H2 less than useful for external analog input purposes.
Those interested in a tale of deck modification might like to visit this thread:
http://taperssection.com/index.php?topic=109703.0;all