Thats pretty low input impedance. Well, shouldn't make a difference.
How can it be E30 is limiting factor when we're see DAC Perfomance Index and it measure very well?
Limiting factor is not the correct way to put it, noise and distortion of both the DAC and amp just have to be added together. However the E30 would be adding more than the DX7 Pro as DAC.
I think in this case it would be calculated like this:
20
· log10[10^(dB1/20) + 10^(dB2/20)] (with phase angle = 0° (?))
Using that formula I get about -107dB combined for my E30 and Atom amp combo,
DX7 Pro (119dB) and L30 (124dB) best case SINAD would be 115dB,
E30 and L30 would give you 110dB.