i got the Chinese boxes (Aliexpress:https://www.aliexpress.com/snapshot/0.html?orderId=8147827966369582&productId=4000164972611&edm_click_module=order_detail&tracelog=rowan&rowan_id1=outfordeliveryV2_1_en_US_2022-04-04&rowan_msg_id=9582814782796635$d9939e06f0f84affaf309b3e43c2b5a4&ck=in_edm_other) and attached them to the negative posts on my Duevel Bella Lunas. Significant opening out of the sound stage in both depth and width, much clearer deep bass and an all around clearer rendering of recordings
On a separate note I converted an old power cable into a grounding only connection and attached it to one of the negative binding posts on my Wavac EC300b amp with similar positive but altogether smaller effect.
Speaker grounding is highly recommended (be careful, though, your amp should be single ended, you otherwise risk shorting it)