If I have read the comments correctly in the thread suggest you have three issues:
1: you say the electronic x-over for the Infinity RS 1b doesn’t have/support XLR.
2: using RCA outputs from DS DAC into your Advance Audience pre-amp the levels are too low
3: sound quality when using BHK250 for mids & high is bad.
Are you using this pre-amp?
The X-Preamp regroups all the classical functions and technology of a High-End preamplifier. The numerous connections allow to link to different sources, Balanced and unbalanced inputs and outputs, MM phono input.
The X-Preamp provides a high-end D/A converter Burr Brown PCM 1796, 24 bits x 192 kHz for Coax, Optical and AES/EBU inputs, as an USB – XMOS input ( asynchronous – XMOS 24 bits x 192 kHz ) in order to obtain from your MAC or PC the better musical performance. Plug your computer to listen audio files, the internet radios as streaming websites in High Fidelity.
The X-Preamp provides a Tone Control as a balance. These circuits can be disconnected via a « Bypass ».
A remote control device delivered with the X-Preamp will make it easier to use…
For better results, use ACS10 : XLR – Balance cable to connect X-Preamp to X-A160
it says you can use XLR connections. It depends how the pre-amp circuits act if you have XLR input but use RCA out.
It might help if you describe your connection set-up.
Eg. DS DAC (RCA out) ->
X-pre Amp (RCA out) ->
Infinity X-over (RCA out/line -level) -> BHK250 -> mid drivers & tweeters.