Cambridge Audio AXR35, NAD D3120, Marantz PM5005 Which sounds best?

I need an amp to power my STAX electrostatic headphones through my SRD-7 transformer adaptor, and pair with a set of M&K mini bookshelf speakers.

I need an amp around 25-60 watts, any more and it will not leave a good enough range on the volume pot to run my STAX.

I didn't know which of the above would be a good solution. I don't want to spend more than ~$300, and I'm a "soft" objectivist when it comes to amps (all solid state amps may not sound precisely the same, but most do sound pretty similar) so I don't expect a huge amount of difference no matter which I pick. Currently, my SRD-7 Box is running off of a Lepai 2020 Tripath amp, but I thought I might want to shoot a little higher than that.

Thanks for your help!
 
The SRD7/SB draws its power from the signal input by the amplifier. I get pretty loud play from my 20W per channel T amp. It has one STAX standard plug that has a Bias voltage of 230 and one at the new "Pro" bias of 580V. Electrostats are strange different animals.

I'm open to some DIY options, particularly down the road as I (finally) teach myself soldering. I just thought that with the money spent on a really good amp, I could probably pick up an inexpensive Receiver or integrated Amp, especially one that has a phono input, though I'm open to suggestions. The ones above I've studied up on. I might even hook up an old Harman Kardon Stereo Receiver. I used to LOVE the HK sound. It's a travesty that Samsung bought them then jettisioned their AV Receivers.
 
The required voltage / resistance for the headphone drive is 8-15 volts at 8 ohms (8-30 watts).
A used receiver / amplifier may need to be repaired, replaced, and adjusted. (((
Take headphones, your sound source and listen, compare ...
Good luck !