Hi all,
I am hoping you can get me back on the right track in the world of Stax. A while ago I bought from Japan an SRD-7 mk2, a SRM-T1S, a Lambda SR Pro and a Lambda SR Signature Pro headset.

The SRD-7 was bought just as an experiment, I did not really expect much from it. Besides I had read that the SRM-T1S should be better. However, from day one I have felt that the SRD7 mk2, coupled to a Pioneer M-22 power amp and a Pioneer C-21 preamp sounds much fuller/dynamic/better lower end compared to the SRM-T1S. The SRM-T1S seems flat or lifeless in comparison. 

I was sure there was something wrong with it, it is an old amp after all. I tried biasing to no effect. I thought that perhaps the capacitors need replacing and have replaced them. No change. I thought that perhaps the tubes it came with were bad and I bought a set of 2 new balanced 6CG7EH electro-harmonix tubes, did the biasing and balance procedures and still no real change. 

What am I missing? What else should I be checking?

The SRM-T1S has been stored for the past 4 months while I patiently waited for my account to get approved on the forum, gave it another go today and impressions remained the same.

That's pretty much how the Stax tube amps sound in stock form... not a whole lot of dynamics on tap there with those tubes and resistors as a plate load

Would the CCS mod be enough? Or are the tubes I got also beyond any hope? 

I am just not sure what would be the wise thing to do financially. Sell the amp and tubes and invest in a DIY amp or start modifying the SRM-T1S?

The voltage limitation of the tubes is an issue but the CCS does wonders to the amp.