I will only be using the dac and amp for my headphones
I already have an amplifier for my speakers.
I don't see how space limitations could be a problem, unless the amp and dac is fricken huge.
My source is my computer, 320 kbps mp3 files.
I have both the HD600 and HE400 running off a new Vali and I really love this new amp. It matches up well with both but it makes my HE400 really shine. My normal amp is an Asgard 1 and I like the Vali better. You won't be disappointed using it with either one. I am using an uber Bifrost as DAC so I can't speak for the Modi.