Buying Audio in EUR and bringing it to the US for resale

Pray tell, who would want a transformer in the path?

I don't know - you could run the transformer into a power conditioner and have a nice 230v sinewave at the end of it. What bugs me is the 50/60hz issue - is this seen as a problem in audio circles?
And I'm also trying to sort out how much of an issue that is in terms of selling price. For example, being in the US, how much would you pay for this 200v Griffon Amp? https://www.audiogon.com/listings/lis9bg1a-gryphon-antileon-power-amplifier-solid-state?creative=305...=
It's listed at $7k. Would you pay 5k? I know I would get takers at $3k, if only to relist it on a european market.

Luckily lots of audio equipment can be sent to mfg - one piece I looked at will cost $500 to get converted, so I'd probably do that before reselling in the states.

Some equipment sold in europe has either external or internal voltage switching capabilities. These would not affect the value in the US. However this must be stated in clear language when advertising. Items that do not have this capability are essentially useless in the US unless a transformer is used as previously stated. Pray tell, who would want a transformer in the path?

England, 230 V, 50 Hz
Can you say what make/models the equipment is?

Yes it will affect resale value if the voltage is not country specific.  Also, some US distributors will not honor warranties or in some cases, refuse to service gray market products.

People in the USA don't want 220V which would need a transformer.