Tube rolling on Leven CS 600

Good Morning.
I have a Leben CS 600 amplifier driving Devore O93 speakers.  I am using Luna Mauve ICs with a Linn Akurate DS steamer, Feikert Volare TT, and Cal Audio Icon Mark ii CD/Heed Abacus DAC. The Leben came with 6L6GC tubes, but can also run with EL34 tubes.
Overall it sounds great but on some older recordings ( mainly CD or streaming) its a tad bright/forward; in part due to the poor acoustics of my room.
I wonder if some tube rolling might be worth a try.
Has anyone any experience/thoughts?

I would look to the signal valves, if it's a tad bright. 6L6 are not really known for being bright. The 6CS7 signal valves, are not a cheap valve either. I would look to GE, RCAs and stay away from Sylvanias, they can be brighter than most (they have there place though). 

If you go to EL34s, you might lose some of the MB/Bass.  They will bring out the mids so the bottom might sound a bit thinner..

Room treatment? Wall and ceiling panels would be a nugget for sure.. 

Your digital sources might be a tad "bright" depending upon the recording. Changing tubes is often a futile pursuit!
For an EL34 alternative try the Gold Lion KT77's a great sounding EL34 variant. Also NOS 6L6 tubes are pretty affordable and might warm things up over current iterations. Also oldhvymec is right the small signal tubes have a large impact on the sound. That's a great little integrated have fun tube rolling!
a great 6L6 family tube is the Tung Sol experience with the Gold Lion KT77 is terrific tone, detail and soundstaging but deficient in the mid and upper bass. The 7581A has stellar bass while being a very transparent bottle.
I've used the GL KT66 in this amp. They soften things a little but also seem to have slightly less in the way of focus with the O/93. It depends on what you are after.
I had the 600 with Devore O/93s. After running various EL34s, GL KT77, KT90, 5881, and the Russian equivalents Jeff Day popularized, I eventually settled on GL KT66, which I found to be the most balanced.
I'm usually not one to put much weight on the notion that cables can transform a system, but: which cables are you using? I find that the apes like being fed with A23 wire.
All that said: the Leben is not a "tubey" amp and in my experience no amount of tube rolling changed that. (Nor experiments with footers, dampers, and incantations.) If your streamer follows the traditional Linn house sound, then it majors on fast and "clean"; I've also found the Feikerts I have (briefly) heard to be somewhat in that direction. Probably not what you want to hear, but them's my 2 cents.
Hi Pingvin,
I appreciate your advice.  But first a question for you.  Are the GL KT 66   "tall " tubes requiring the lid off approach?
So my system has evolved a bit since the first posting of this thread.  My Linn is now a Rockna Wave Light DAC and a Bricasti streamer.  My IC are Luna Mauve.  My speaker cable is a bit of a problem- as it is in the wall and had to follow RI building code ( thats a bit of a joke )- Tributarie.
I usually ran the CS600 with the lid off, but I recall -- I haven't had it for a few years now -- that the GL KT66 were able to fit below the lid. 
The upstream components don't look to be at fault. I've only heard one system with the Luna cables and it certainly didn't have a harsh sound; based on the company (dealers) they keep, they seem very compatible with the Leben and Devore. That leaves two things: your cables and the room. Can you experiment with, say, some Luna cables and changing speaker position, at least temporarily?
I’ve owned Devore speakers since 2008 including the O/93 for 6 months or so. The mids on that speaker were not for me. I tried a couple amps and the A23 before moving on.
It has been mentioned that the coupling capacitors can easily be changed to effect the sound signature as well.  The 1.5uF caps can be changed for something with more body (Jupiters?) or the value may even be bumped up a little for a bit more roundness/fullness though articulation may suffer.  Anyone have experience with this?

Has anyone used the JAN Philips 6L6GWB?

If so can you comment on its tone and midrange?