Replace Silver interconnect cable , please advice

I see 2 things you may want to look at. First is break in. Cardas takes a very long time. Second is your PC. There's a very good chance setup is not as good as it can be for audio. If you haven't already done so, try comparing a ripped CD played through your computer, to playing the actual CD in your Oppo. See how big the difference is.

I would guess it probably has to do with your speaker placement over anything else. That is really good gear you have there. Your source is probably the weak link if you have one. Acoustic Zen Silver ref is a good cable. It's not the problem at least not to the degree you are describing. Some rooms are very tough to get good sound in.

Also possibly something could be amiss with your computer setup and delivery to the DAC? Have you tried just playing CDs in the Oppo?

If you are looking for a different flavor you might try Grover Huffman cables. They are very cables and a great bargain too.

Ejlif:
"Your source is probably the weak link if you have one"

you mean the DAC (oppo) or the PRE ?

when i play CD it's much better then the computer
but even then it's not so good.
i even though to replace the speakers with Utopia Scala or something else.

make sure your speaker settings in the oppo are correct for two channel listening with no subwoofer.

If the pc and oppo is your only source, you mayhave a setting issue in he oppo.

Does it sound like bass could be better or like something is "wrong"? I have the older Focal 1037 Be and also have an Oppo 105 and have never had weak bass in a pretty open room with high ceiling. I have tried Home Depot 14g copper extension cable as speaker wire (just for kicks), Anticables (copper) and Analysis Plus Big Sliver Oval, which range from $25 to $1000. All of them sounded different and had different presentation and definition of bass but all were enjoyable in thier own right and none gave the impression something was "wrong" I suspect the DAC/PC or other electronics or the room/placement.
I agree with playing a good sounding cd or sacd on the oppo and comparing to the PC. If the Oppo sounds better, look into your pc set up. I have used the Oppo Dac with great results with a Mac Mini and Pure Music.