Is there better pre-amp for "bi-amp"ing ?

I am using GFP-750 to drive two Levinson 333 + Nautilus 801.

- unbalanced output is driving the first 333 to bass section
- balanced output is driving the second 333 to mid/high sections.

I tried Anthem with similar configuration but the output level between balance and un-balance are off by 6dB so can't do.

I tried Audio Research pre-amp and use Y - connector to drive both 333s. It seems the output driver of the pre-amp is not designed to be loaded with two paralell inputs (two AMPs) so the sound dynamic is lacking.

Has anyone experiment with bi-amp and found improvement over single amp? What pre-amp did you use?

Sounds like you need an active XO. check out Behringer DCX2496 mods from Scott Endler. YOu will need to be able to bypass (or defeat) your speaker XOs.
Bat vk51se has two sets of balanced outs as does a levinson 32. both would work fine.
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If you're using the GFP in passive mode, it's the source that would be the problem.

When using identical amps in parallel, the combined input impedance is reduced by half. The GFP has an output impedance of 600 (RCA) and 1200 (XLR) which, by the numbers, should not have a problem driving 25K input impedance. The 333's have twice the impedance for XLR vs RCA and probably more gain as well, so you got me stumped how that works decently. Combining RCA and XLR can mess with the CMMR (noise reduction) of the circuit.

I've successfully biamped with much lesser and more diverse gear than yours but it hasn't always been easy. Currently, I have 3 amps (nearly 3 KW combined) with a passive TVC, so anything is possible.

Inserting an active Xover is more complicated than it may seem and will require technical knowledge as well as possible surgery to the speakers but that is the ultimate.

I know the 801's are power pigs but do they really need dual 333's. I'm not one to talk and I'll agree that most systems are underpowered, but is it really worth YOUR trouble?

Another possible option is bridging the 333's and using them for each channel. That can result in 4 times the wattage but not all amps can be bridged successfully, espescially into low impedance speakers. Contact Levinson if that's advisable.