Electra Print 300B amplifier - Help

I happened to own Electra Print 300b monoblocks (2 300b per side) and what I assume is UltraPath Line amp - preamp with 6j5 signal tubes and 5v4gt rectifier tube. Very nice amps and preamp - keeper.
link to pictures below:
picasa album - click to open

Amplifier and matching preamplifier sounds fantastic and I couldn't be happier, however. I am a bit worry with limited information about this particular amp. From what I gathered and read about Jack Elliano’s Direct Reactance Drive Amplifiers and his products is that most of his work is custom and that he usually builds around specific tube(s). Circuitry is tweaked and optimized for that specific tube(s) and that's how my dilemma began. Simply speaking, I have no idea what 300B tubes are used in this amp and if I can swap those with other new production tubes or something more vintage like Svetlana Winged C ? These tubes resemble in construction cheap, Chinese imitations of WE 300B tube but have no markings other then "300B" right in the middle of the glass.

Another concerning issue was mentioned in Enjoy the Music review article of similar amp. Here is small fragment from that review, describing that nitty gritty problem:

" The Electraprint  has one problem. Not with the sound and normal operation, but with the biasing. Because of its setup, biasing is done by moving a connector on a variable resistor and then measuring the voltage drop change across a 10 ohm resistor. Problem with this is found inside the chassis where it is difficult to reach unless the amplifier is turned over. Therefore it is difficult to do with the amplifier in the system. Second, the variable resistor also controls the voltage to the driver tube and the two interrelate. Thus as you change the output tube bias the driver tube voltage changes. "

If anybody has any info about these amps (and preamplifier), tips, etc. please share your thoughts.

(BTW other tubes used in these amps are small radio 6an4. Also, I emailed these questions to Electra Print, Jack Elliano but was referred to circuit page on their website. Unfortunately, I am not that advance and it really did not help me in any way)

Thanks in advance

Never worked on a DRD, but have scratch built a Loftin-White as well as OTL, SET & etc. If you look at the schematic on the E-P web site for the single 300B version (closest one to yours I see) it uses a Sovtek 300B. Biasing instuctions are on the schematic: first you adjust the 300B bias, then with the other adjustment, adjust the driver voltage. I assume you have a 2nd adjustment for driver? Since the amp is direct coupled, each adjusment will effect the other, so you'll have to repeat the adjustments a few times. If there's no adjustment for the driver tube, you'll likely have to do what I have to do with my L-W, ie. try several different driver tubes until you get one that gives the right voltage. You'll obviously need to flip the amp over to do this work. You'll need a voltmeter & a dummy load resistor or a cheap speaker to load the output. If you don't feel comfortable working around high voltages, by all means take the amps to a good tube amp repair person.
Jack primarily uses the Sovtek tubes. So a Sovtek 300B should suffice. I live near Jack and just came from his shop as we're working on some things together. I'll print this off and call him to see if I can get him to be more specific about what you need to do.

However, if this is too technical for you, as suggested take the amp to a competent technician. Jack's circuits are not complex so anyone who understands tube circuits should be able to help you.
Would it help if I could link to better pics of that particular circuit?
Thanks for your feedback guys!
Yes it would help.