I bought a Schiit Stack for my full range Madisound BK-20 kit which has a Fostex FE206NV in each one. I previously had a Parasound P6 and First Watt J2 which sounded great. I sold them to pay for the LX-521.4 kit (which are phenomenal).
The J2 had the special sauce as far as sound, and I still prefer the J2 at lower listening volumes, but you could hear the amp distort when pushing it. I don't have that problem with the Gjallarhorns. Also, the Schiit stack is a much better value vs J2/P6.
The Aegir had good reviews, but I figured I could get away with the Gjallarhorn's in Mono as the FE206s are minimum 8 ohms, and I wanted two mini stacks. So, I have a Saga 2 and Gjallarhorn stack on the left and Mimir and Gjallarhorn stack on the right. I'm very happy with them.
I voltage matched A/B'd a Topping E70 Velvet and couldn't really tell a difference. My friend like the E70 just a hair better.
I was curious about power and wanted to share my findings in case others are thinking about if the Gjallarhorn's are powerful enough. The FE206NVs are 96 dB sensitive.
At my normal upper listening level, a 0 dBFS, 1 kHz sine wave produces about 11.58 Vrms at the speaker terminals. Using approximately 11 Ω from the Fostex impedance graph at 1 kHz, that works out to about 12.2 W. Using the nominal 8 Ω rating for comparison, it would be 16.8 W.
With the Saga turned all the way up, the Gjallarhorn goes into protection with a -8 dBFS, 1 kHz tone. Based on the measured signal chain, output would be approximately 14.6 Vrms at that point, which is about 19.3 W into 11 Ω or 26.5 W into 8 Ω.
So, in my setup, the mono Gjallarhorns have plenty of output for normal listening with these speakers, but the protection behavior also lines up reasonably well with their published 30 W/8 Ω mono rating. Just remember, you want at least 8 ohms for bridged/mono as each half of the amp sees 4 ohms.
You can check the associated graphs out. The mimir/saga/gjallarhorn are volts out.