ibmcom: Official ROM is a must, because you need to have all base essential files, like drivers, etc. to match your device. Extract some official ROM using some visual kitchen (I am using one from ervius). After that, just try to cook it without any changes and flash your device (after HardSPL of course). If all will goes without problems, you can try to change some EXT packages and so on. The last step and most difficult (well not really, because developed tools make all much easier) is porting of XIP.
If you will succeed with all of this, you can play much more with you ROM, like deleting and editing some files from OEM and SYS. Good luck!
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CHII > HTC S710 Vox, WM 6.1 CLEAN v1.4 by fireburned
MICHIRU > HTC Touch Cruise 09 (iolite), tO's lite WM 6.1 ROM XIP 21054, BIG thanks to OliNex