This is my current go-to amp setup. The Alembic F-1x preamp running straight into the "power amp in" on my modified Guild Thunderstar Bass amp (dual 6L6 + 4ohm OP transformer) into a Genzler 2x12 4ohm cab.
Some years back I used to own a stock Thunderstar Bass amp and absolutely loved the tone, but with the stock
8-ohm-load-only power section, paired with any of the affordable 8ohm cab options that were within reach for me at the time, it just couldn't put out enough clean volume to match a drummer. Now though, with a super efficient modern cab like this Genzler and the flexible EQ of the Alembic preamp, the modest ~45watt power section of this 4-ohm-enabled Thunderstar has truly epic levels of clean volume on tap! Perfect for my 3-piece jammy outlaw country rock band. On the off-chance we do end up playing a larger gig without PA support for the bass, I can always just run my Alembic preamp paired with my Stewart 1000watt power amp.
I should also note, the Thunderstar preamp sounds plenty good on it's own, but the EQ is rather limited and of course it doesn't have an XLR out either, so working the Alembic into the rig just seemed like a no-brainer.