Well you can wait another month and buy both at the same time. Tzeentch is a patient schemer, not the type to rush out screaming BLOOD FOR THE BLOOD GOD, SKULLS FOR THE SKULL THRONE GRRRRAAAAAAAAAAARRRRRRRRRRRRHHHHHHHH!!! all because the whole point only is to spill blood (or bleed cash), as Khorne doesn't mind whose blood it is that gets spilled.
Not sure how similar they are, but in terms of amplification you can safely assume that what can drive that well shouldn't have issues on the HD800S. What did the shop have on it? You can just get that if you already like the sound.
Alternately, order the HD800S, and then try it out at the shop with the same amplifier. If you like it then get that one, safe bet considering you've already heard it, unless it's a low end amp and you're willing to try and see if the improvements from a midrange (in terms of price) amplifier would be worth it. That said if that was the HDVD800 and you can afford it without eating instant noodles for weeks, I'd say go get it.
Do you have a CDP or a DAC? The HDVD800 has a DAC in it on top of the headphone amp.
DAC-HPamp:
AudioGD NFB-11
AudioGD NFB-29
Burson Conductor
Violectric V200/V281 (Go to German website where you can order an optional integrated DAC module with the amplifier)
Headphone amps
Schiit Valhalla2
Meier Corda Jazz FF
Meier Corda Classic FF
Burson Soloist
AudioGD Precision 1
WooAudio WA6SE
DACs
Schiit Bifrost
Meier Corda DACcord
AudioGD