Chris
Yes you are right red cables are signal right, blue are signal left, all signal grounds are linked together with a lead from them going back to the star ground point in the ceter of the Cap6 filter.
In a pre amp you would normally have the one point in your system where you also make a connection between signal ground and chassis earth but this should be the only point in your overall system where you have this link or you will create an earth loop and get a mains hum.
Some people also fit a switch in this ground to earth connection so you can lift this connection in the case of a Hum from say a problematic source complonent, you could even fit a 3 way switch so its either
1 connected
2 lifted
3 connected via a resistor or diode/cap/resistor network.
Note that the left hand switch is a Goldpoint 24 point stepped attenuator Vol control
again another shot for clarification
IMG_2375 by Alan Towell, on Flickr
Alan
Turntable - Garrard 401/Jelco 750L/Ortofon Kontrapunkt B, Pioneer PLC 590, Micro Sieki MA505 , Denon DL103R - DIY Paradise Phono stage - Reel 2 Reel Studer A810, Otari MX55,Tascam BR20, Revox A77, B77, PR99, TEAC X1000 & 3440, Digital HTPC / Young Dac - Preamp - DIY B4, 821, Power Amp's DIY Avondale NCC300 Mono Block, Speakers Wilmslow Kit Volt BM220.8 / Scanspeak D2905/9500