Firewire/USB2.0 combo for DVD burners, which one?

I’ve tested three different ones with my DVD Burnes on PL-3507 enclosures and all did not meet the specs. I need the combo Firewire/USB2.0 since my 3 years old P4 2.0 GHz does not come with USB2.0 and all other slots are full.

I’ve tried the following:
1- Adaptec AUA-3020 Firewire/USB2.0 combo, 2 years old.
Firewire chipset is Texas Instrument. Underspec in my P4 2Ghz (21 MB/s on BenQ EW164B BEFB and 24 MB/s on PX-716A), works fine on P4 3Ghz (24 MB/s on EW164B and 27MB/s on PX-716A)
2- Adaptec AUA-3020CS Firewire/USB2.0 combo, newer model with power connector.<O:p</O:p
Firewire chipset is Agere (AT/T Lucent). Did not detect my DVD Burners at all.
[color=black][font=Verdana]3- SIIG JU-2NE012 Firewire/USB2.0/LAN combo (newegg)<O:p</O:p
Firewire chipset is Texas Instrument. Burst rate is fine on my 2Ghz machine: 24MB/s and 27MB/s on EW164B and PX-716A respectively but cannot maintain throughput, write speed ok up to 12x and drop down.

Anybody can share your experience using a combo card on older PCs? What brand and model that works for you?[/font][/color]