Attenuator recommendations

You might want to get in touch with Marchand Electronics. They have a good selection and can tailor to your needs.

The XLR/RCA presents a difficulty because to be fully balanced means double the components. On the other hand, TVC's don't care about balanced or SE. Either way, you're essentially talking about a passive preamp, in some form.

The Pass amps have a low input impedance that can be difficult for passives but should be good using XLR.

It occurs to me that all you need is resistors in male/female adaptors. How's your soldering? You might start with 3 KOhm and see if that works. To give you an idea of the rating, P=V^2/R, so 1 watt would be more than enough. If you can find Vishay at 1% tolerance, you're cookin'. You can't get more direct than that without cutting into the IC's.

RCA requires only one resistor on the positive (inner). XLR needs two. If I'm remembering correctly, (it's been a while) terminals 2 and 3 are hot while 1 is ground.