Allin,
Purchase an upgraded ZW from Jim here on the OGR, for conventional either the 250 or the 275 are proven power houses for conventional running. I also like the Z4K but remember they are really just 2 channel Transformers as far as running goes. The old ZW's are 4 channel train runners. I would get a couple of them, in fact I own 4, two of each.
PCRR/Dave