I agree that it is likely the 4060s overloading. For stack taping, 4061s or even 4062s are a good idea.
Okay, close stack taping may reach a level where 4061 are required.
the 4060's should be AOK when powered correctly, the specs for the 4061's are 144 dB SPL Before Clipping, 4060's are 134dB SPL
It's not nearly
as difficult to overload these mics as you would think. DPA specifies 134 dB max SPL, but that's not
an RMS A-weighted rating.
Here's DPA's explanation (LINK
In many recording situations it is essential to know the maximum Sound Pressure Level (SPL) the microphone can handle. Please note that in most music recording maximum peak SPL's easily supersede the RMS value by more than 20 dB. The RMS value indicates an average SPL and will not show the true SPL peaks.
If you're taping on the stacks and a traditional SPL meter reads 105 - 110 dB (usually measured at the board), peak SPLs at low frequencies can easily approach and exceed 134 dB.
In this situation, a preamp is not needed. In fact, I would say it's borderline suicide. You would be much better off with a battery box and the adjustable gain of your recorder's line input. I'm not familiar with the CA-9100s circuitry and what it's doing on various gain settings, but can only assume it's passing the signal through more circuitry than needed.
A simple 9v power source w/ good quality dc blocking capacitors is all that is really needed and more akin to a 'straight wire.' Adding a preamp device with moving parts, higher current drain, etc. can only create more points of failure. Without question, I think a simple battery box is the better tool for this specific task.
I have run into brickwalling issues running line in to my DR-2D using Schoeps MK4 and RBox twice. The RBox runs a hotter signal than the NBox which has never had the issue. The gain on your pre-amp may be the culprit.
Finally, we do need to consider the recorders maximum input level. I don't think it's the gain on the preamp because you mention it only distorts on the bass / kickdrum, but Daspy's experience here is correct. A 'hot' signal can definitely overload the DR-2D input.
Luckily, we can discuss a recorder's maximum input leve in exact voltages and compare it to other recorders. From the DR-2D Manual:
LINE IN jacks
Connector: 1/8” (3.5 mm) stereo mini Input impedance: 22 kΩ
Nominal input level: –10 dBV (0.32 V)
Minimum input level: –22 dBV (0.08 V)
Maximum input level: +6 dBV (2.0 V)
In terms of input overload resistance, +6 dBv isn't bad, but could be exceeded if an external preamp is used. I'm not going to go into huge detail on this, but let me compare to the line inputs of a few other recorders.
Sound Devices 7xx Line input: +26 dBu (+23.78 dBv)
Roland / Edirol R-44: +24 dBu (+21.78 dBv)
Sony PCM-M10: +6dBv (listed as "Rated input level: 2 V" in the manual specifications)
You'll notice a pretty big difference with the two 'professional' recorders with balanced inputs, but the DR-2D is on par with the venerable Sony M10, which is pretty touch to overload. It's not fun, but I can run a fixed gain pre like the PSP-2 (or Nbox) in front of the M10 for most shows. Dinosaur Jr, perhaps not, but most are fine.
This is in contrast to some handheld recorders with much, much lower input clipping levels. For example, the original R-09. I can't find the exact specification, but it was much lower than +6 dBv and would easily clip with an Nbox.
Huge bummer that the seller mistakenly sold you 4060s. I have no doubt they are the cause of your stack taping woes.