The Markbass heads do pack a PUNCH in the volume in the department and I will agree the WT 550 runs out of steam WAYYYY too fast. If you use the Eden head, I suggest turning the low frequencies below 80hz down as a default setting.
I thought the WT550 sounded great though, but much better though with a 4 ohm load or at least more speaker cabs.
If you like the Markbass stuff already, I suggest going this route right away. There is very little reason to not go for Markbass unless you hate the tone produced by the heads (like I do!

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