If you want true transparency, then your best bet is a decent DI box, an audio interface (if you want to record) or a good-quality mixer with a foldback (monitoring) system. I am totally digital, so I would go with a DI, interface and then my headphones (AKG K701). So, Bass-DI-Interface-Foldback or Bass-DI-MixingDesk-Foldback.
Whether that's actually useful in determining how a bass would perform on a real gig is another issue. If you want to determine that, then a couple of popular amplifiers would be a good idea. An SVT, a MarkBass, a Genz-Benz, etc. It would get very expensive though!
The advantage of the first system is that you would have a more neutral setup. It would also be cheaper. A decent DI would cost you $100-200, perhaps less. A small high-quality mixer would be relatively inexpensive and a pair of monitoring headphones like the K701s are around $200. If you went with the interface option, you might be able to dispense the DI (some had a high-impedence input) but you would need a computer. Anything would work reasonably if you're only using one channel. I would be considering an Apogee Duet but there are cheaper options for an interface.
Last edited by GrumpiusMaximus : 12-23-2013 at 04:49 PM.