Thats a good option with 2 Tascams, we have 2 SONY HDV FX1 cams, optional each cam with LANC to SMTP timecode Radiotransmitters, all in Sync.
I trust more in Tascam than EDIROL to make good sounding devices. The stock TASCAM is better than the EDI i guess.
2 Microtracks needs Soldering to make them START STOP from a single Button and no SMPTE timecode.
Edirol R4 Old model was a bit dull, not fast in transients noisy on highgain analog. With the Apogees oit was was better, the Harddrives in generall are more destructive to sound then CF cards. Stupid Design only 2 Channels on SFDIF IN and the other 2 are lost.
The R4 Pro is TIMCODE IN and OUT, TASCAM only OUT.
The price EDIor Tascam is not so a big problem but Soundevices is to expensive.