HELP requested for system setup analogue source

Hello all,

After his relocation, I have been busy for a week in order to help my nephew setting up his system. Disappointment all over concerning analogue sound reproduction. Could you please help us out here ....

Given is the following system:

SME 20/2 turntable with SME V gold arm
Ortofon Rohmann select cartridge
Ortofon N8 copper interlink (blue)
Mark Levinson 25 S phono preamp
MIT 350 proline reference interlink
Mark Levinson 380S line preamp
Nordost Valhalla balance interlink 30 ft
Mark Levinson 33H power amps
MIT Shotgun Oracle V1
Avalon Eidolon speakers

Problems:
Power amps are humming (not over speakers but in power amps themselves;
Sound far too airy, hardly any bass. For CD reproduction sound is 'okay' for now.

Any suggestions?

Thanks guys ...