Higher voltage servo motors with low volt drivers

I posted a thread a couple of days ago, indicating my need to change an old
controller on a medium size bed lathe with a setup of Turbocnc and Gecko
320.
Motors are as follows:
Servo motors are Siemens with the following specs:
- Dc Servo, permanent magnet.
- 1.03 kW
- 2000 RPM
- 176 V
- 7.1 A
- Max. torque 5 Nm
With an optical encoder, +5v and 1024 count/turn.

I received a couple of replies one indicating that I would loose a lot of
speed as Gecko's max voltage is 80V, and the other is that I should try a
copley driver.
I took a look and Copley drivers, I got a little lost as my Electrical
background is not so good, but I think they do not accept Step&Direction
from a PC.
My question is, if I'm willing to sacrifice the speed, will the Geckos run
my motors, what about the torque??? will I loose a lot of torque???
And regarding the current will it be suitable to run 7.1 A with Geckos???

I'm doing this for the first time, so any help is truly appreciated.

Mina F.