just browsed the forums and at the moment not many gems around, except for these few:
Dynaudio 240mkII speakers RM1500
http://www.mycarhifi.com/carhififorum/viewtopic.php?t=4401
Helix A2 Amplifier RM2200
gr8Tunes.net - Car Audio Forum - [FS] Helix A2 competition class A amp
Arc Audio XXK4150 Amplifier RM1800
http://www.mycarhifi.com/carhififorum/viewtopic.php?t=4315
Steg QM 310.2x amplifier RM2100
Steg QM 220.2x amplifier RM1600
http://www.mycarhifi.com/carhififorum/viewtopic.php?t=4450
USAmps TU4360 4ch Class A tube amp RM1250
Bravox 12" subwoofer and box RM650
http://www.gr8tunes.net/forum/showthread.php?t=8637
RS Audio Component speakers RM1200
Genesis 12" Subwoofer and box RM900
http://www.mycarhifi.com/carhififorum/viewtopic.php?t=4415
JL Audio 12w3d1v4 subwoofer with box RM950
a/d/s P450.2 amplifier RM1100
http://www.gr8tunes.net/forum/showthread.php?t=5860
RF 250m monoblock amp RM850
http://www.gr8tunes.net/forum/showthread.php?t=8862
PG Xenon x200.4 amplifier RM1600
PG xenon x600.1 mono amp RM1200
http://www.mycarhifi.com/carhififorum/viewtopic.php?t=4333
Peerless XLS 12" sub RM850
http://www.icehifi.com/index.php/topic,925.0.html
DLS UR36 3 way component set RM1000
http://www.icehifi.com/index.php/topic,1148.0.html
Xtant 2140c amplifier RM800
http://www.gr8tunes.net/forum/showthread.php?t=8871
Precision power A600 amplifier RM900
http://www.icehifi.com/index.php/topic,1155.0.html
Genesis Dual Mono Amplifier RM1800
http://www.mycarhifi.com/carhififorum/viewtopic.php?t=4416
PHD FB12.1 subwoofer with box RM850
http://www.mycarhifi.com/carhififorum/viewtopic.php?t=4310
DLS subwoofers RM2000-2300
http://www.mycarhifi.com/carhififorum/viewtopic.php?t=4377
Mcintosh Component set RM9++
http://www.gr8tunes.net/forum/showthread.php?t=8820
Image Dynamics IDMax subwoofer RM900
http://www.icehifi.com/index.php/topic,1113.0.html
Precision Power A404.2 amplifier RM800
http://www.mycarhifi.com/carhififorum/viewtopic.php?t=3895
i think with your 6k budget can get something like this......
dynaudio speakers, genesis dual mono amp, genesis sub and RF mono = RM5050 and got extra for good cables...
or rs speakers, helix a2 amp, phd sub and pg mono amp = RM5450 also got balance