Here’s a comparision of my line stats between the two filters I’ve tried…

  Downstream Upstream
Original inline + double adaptors
SNR Margin 6.5 dB 13 dB
Line Attenuation 47.5 dB 25.0 dB
D-Link DSL-10CF (no double adaptors)
SNR Margin 7.0 dB 12 dB
Line Attenuation 47.0 dB 24.5 dB