congratulations on your Eventide and welcome to the forums!
The optimal place for a digital fx processor is always between preamp and power amp. In your case there's not much you can do other than use another couple of loops (for stereo) to connect the Eclipse to your gtr amps front inputs. Obviously using distortion from the amp is not recommended.
Eclipse uses 1/4" jacks for unbalanced -10dB instrument levels I/O and XLRs for balanced/unbalanced +4dB line levels I/O. You should use the 1/4" jacks in your system.
You may want to check our technotes out, on the Eventide website, regarding gtr rigs tips and I/O wirings.