I usually just use Nero 6.6. I had a look at the 1673 review thread and saw a link to CDRINFO also stating C2 problems with burning CD media.
But they found out that using Verbatim at 40x, which is the media I usually use, gives good quality burns.
According to CDRINFO the Liteon 1673 cannot copy Securom above 2.8 though, but I saw that you use 1693 firmware, so that could be the trick for the copy protection.
I wanted to have a look at the memorex (rebadged 1673) review, but the cdfreaks server isn't reachable atm.
Actually I feel drawn towards the Benq 1640 for all it's good features, but if the Liteon proves to be stronger in the CD burning department I will stay with Liteon.
Thanks for all the effort!