I guess most of you are aware of the compatibility issue of a plextor DVD burner and most of the external enclosures in the market. Here is my experience ( all my enclosures were purchased from dealsonic.com):
chipset of the box and result:
Ali chipset (e.g. Sapphire): not compatible, unable to start recording at any speed. This seems to be insufficient power due to the weak power adaptor supplied with the box;
Myson chipset: can burn but always buffer underrun even at 4x. Burning a disc took longer than 1x with IDE connection
GL811 chipset: Same as Myson
NEC chipset (e.g. Syba): Better than Myson but still buffer underrun at 8x
Prolific chipset (e.g. Plumex): Stable at 8x, however, this chipset has compatibilty issues with the USB ports on my Dell Dimention 2400's MOBO. Only a stand-alone PCI USB card 2.0 with NEC chipset can accept it. (This result may vary as I have 6 USB devices plugged into the MOBO)
Overall, it seems most USB to IDE bridge chipsets cannot handle the transfer rate of a DVD burner ( ~22MB/S at 16x). The IDE cable is not an issue here as all of them uses 80-pin cable.
However, it is mysterious that my Pioneer A07 can burn 8x even with the low-end GL811 chipset. Did plextor lock their drive? The requirement of the power supply is also critical for plextor. My recommendation: use Plextor internally if possible.
P.S. All the enclosures I bought has a common problem: their "ball-bearing" fans are actually one ball + one sleeve bearing. They last no longer than 3 months. I replace all of them with Delta two-ball bearing fans purchased from Ebay. You may simply disconnect the fan if you do not like it. But for certain enclosures with integrated PSU a fan is critical.