Understanding phono stages/What to look for?

Everything from little boxes to full size components. Very few reviews. What should I look for. I have purchased a Black Cube to use with a 30 watt tube integrated. Although I have not been home yet to audition any of it. Why the huge differences in phono stages? I am using a Nottinhgham Interspace w/Rega tonearm OM20 switching soon to a Dynavector 20 low output MC. Will I want to stay with the Lehmann? Lots to learn, Louis
I have been using the BC on one of my systems for four years now. I am considering only the optional power source. I like the easy settings, and the sound is great. On my high-end system (read: high-for-me), the Linn has one for twice as much that is made for it and tucks nicely inside. And, similar to yours, my BC is being used with a 35 watt tube integrated. So I doubt you would want to consider anything else unless...
But the huge difference comes from the relatively new need for them in a, thank God, growing market for fifteen unbroken years. I have heard great stuff from the outboard CJ, but I feel no lack in the Linn. If I had another table in my best set, I would seriously consider it.
The OM20 cartridge you are using is not really suitable for the Rega arm.The Dynavector will be a much better match and then you will begin to hear what your turntable can do.The phono stage you have is very good but obviously the more money you put into something like a phono stage the better it should get.As it stands I think you will like what you hear.Look through the archives here and you will glean much info on phono stages and matching different components.
The PWX power supply will transform your cubes into monsters for a very resonable price. I and a friend each had BCs with the power supply upgrade with great success (I also used a Dyna cart- you'll like that too). You have to spend A LOT MORE $$ to get appreciable gains over the Black Cube with the PWX power supply
Stay with the Lehmann. Quiet, clear, dynamic, handles any cartridge. I kept the Cube in rotation with several high-buck phono stages over the years (Herron, cj premier 15, Xono) and it never embarrased itself. Often I preferred its deep tight bass and black background to the tubed units. Still have a PWX version (I cannot say it is THAT much better than the wall-wart version) which has finally been humbled by my current Groove and Ear 324. I haven't looked around at lower-priced phono stages for 10 years or so, but I do believe the Cube is one of the great values in audio.
Many of the low end SS phono stages sounded more compressed than the tube gear version. BC isn't that great when it was compared with all my full function tube preamps. It is nice and quiet but very harsh and distorted highs. Even the the bass got beaten by some vintage phono sections in both MM and MC. It was no better than the cheap SS phono section either ( except it has MC.) However, it is usable for less $200 in used market. Nothing to write home about it and don't expect it to out beat a $400 CD player either.
You should go through many of the threads here about amplication for the cartidge.
Musical Fidelity makes a nice tube phone stage for about $400. If can't find a local dealer you can order it from Music Direct which has a no questions asked 30 day money back guarantee.

I agree with S23chang the Black Cubes have very nasty high frequency problems - ba d bad treble with revealing amps / speakers.
I'm surprised no one mention the Dyna P-75, an obvious good match for the 20
I still have the Black Cube but I have purchased the Lyra Dorian instead of the Dyna. Have not had a chance to use it as I have just moved. I want to spend sometime with my old cartridge in my new listening setup before I put in the new one.
After looking at many phono stages (inc Aesthetix and Lamm) I came down to two units: the very good unit from Decware would is about 1550 (MM/MC capable) and is a tubed unit. I would up ordering a Dynavector P-75 as I have heard nothing but good things about it. If the Dynavector proves inadequate for me then I'll spend the extra money for the Decware unit.

I try to avoid tubed units that have a bunch of tubes in them (Aesthetix, BAT) due to the cost of acquiring high quality NOS tubes. The Decware uses a small number of tubes and is built extremely well as all Decware products are.