96kHz at 24-bit is ~288k/sec. 72 tracks of that is ~21MB/sec which should be no sweat for an internal SATA or eSATA drive (they are for all intents identical unless your external enclosure has a horrible controller.)
I just imported 53 stereo tracks (so 106 effective tracks on paper, but it’s not quite as bad as 106 independent tracks since the two channels are interleaved…) at 96khz/24bit from an eSATA disk and while it’s a cacophony of noise (they were all songs) they all play back no problem… about 30MB/sec. The disk-o-meter in the VST Performance window (I’m at home on Cubase) doesn’t even light up, I’m not even sure it works 
A speed test on the drive gives well over 160MB/sec (sequential), a 3TB Seagate drive stuffed in a generic Sans Digital enclosure I bought.
Now for USB2 and Firewire 400, 20MB/sec is starting to approach the upper limit on sequential reads for most externals I encounter… and writing is always slower. For Firewire 800 or USB3 that many tracks shouldn’t be a problem assuming a decent external drive and controller, not crappy little 2.5" bus-powered drives which are pretty slow no matter what they’re connected to. However there are other issues to consider than just drive speed particularly for USB/Firewire, like if they are on the same physical bus as your audio interface if it happens to be a USB/Fireware-based interface. Lots of variables.
I don’t have 128 independent channels to source, but I just made 128 tracks set to the same mic input and hit record, to the same eSATA drive, and it doesn’t seem to care. Still writing to 128 96khz/24-bit files at once, even though they happen to all contain the same data.
So yeah, I’d analyze your hardware setup a bit – see how your new machine behaves.
(FWIW I did the above tests at home on an HP z600, 6-core 2.66GHz, afore-mentioned eSATA drive connected to the motherboard’s SATA controller, on Windows 7 x64 Cubase 7.5 with a Focusrite Scarlett USB2 interface.)