Exactly what gear were you running. I guess since you mentioned bass roll off and SP, one of their pres? Generally speaking, I want the most gain to come from my pre and use the recorder for tweaking the levels. Of course it does depend on what gear your using. If your using a high end pre and a handheld recorder, for example, you'll most likely get much cleaner gain, less noise, from the pre. Regardless of the specific gear, if you had your recorder cranked all the way up, I'd bet on that being your brick walling cause. I can't imagine why SP would recommend turning either the recorder OR the pre all the way up. That's asking for noise floor issues, clipping, etc. However, you did mention that you were balancing them out at 50/50.