later this afternoon, i was doing some more experimenting with the ISA430MKII . i ran my bass into a Radial J48 direct box, and into the ISA's mic pre (powering it with the +48 phantom switch) instead of the front panel instrument jack.
the ISA has four different mic 'impedance loadings' to choose from, as well as an 'air' button that opens up the high end a bit more. the second to the lowest impedance setting is the ISA 110 setting, so you have 1 lower one and two higher ones, all effecting the instrument's 'voice' . pressing 'impedance' steps through each of the four transformer pre-amp input impedance values, as indicated by their corresponding LEDs. by selecting different values for the impedance of its transformer input, the performance of both the ISA 430 MKII preamp and the microphone/direct box can be tailored to set the desired level and frequency response.
this really opens up a whole new world of slightly different colors as a bass preamp. i was able to get a more 'open' and transparent sound as opposed to using the inst. jack, which is more discrete solid state sounding (but still awesome). i was even able to dial in some 'tube sounding' grit if i wanted it. at one setting, i had it sounding like my '69 SVT.
the 'vintage' compressor and limiter settings also allow you to get some vintage grind in that stage too. there's also a 'balance' knob, where you can blend the compressed signal with the uncompressed one, and that's the way that i've been using it lately, since it still retains all of the punch and attack of the orginal uncompressed sound, but also adds a bit of sustain and fullness to the slightly dead spots on my fender basses.
so, IMO, this is really a 'deep' unit that has alot of ways to dial in a really big & fat bass tone, and i'm just starting to appreciate what it can do.